The quarterback put on a brave front, but he couldn’t prevent the threat of another concussion from entering his mind. Scrambling for a first down and facing a group of defenders, he wondered if another yard or two was worth risking another head injury?

Trent Green played 11 NFL seasons, including his first two with the Washington Redskins. He mostly shook off injuries, but there were lingering effects — mostly in his mind — of a severe concussion he suffered in 2006.

“When you get out in the open field and you’re running and you see three guys coming,” said Green, who retired after the ’08 season, “instead of saying, ‘Okay, I’m going to get this first down,’ it’s more: ‘You know what? It really doesn’t give me much of an advantage to go against these two or three guys.’

“I guess it does change your frame of mind a little bit.”

After Redskins quarterback Robert Griffin III suffered a “mild” concussion in Sunday’s loss to the Atlanta Falcons — a debatable description, according to a physician who independently evaluates Houston Texans players — the questions circulating throughout the league are whether the injury will change Griffin, and how much it will compel the Redskins to change around him.

Griffin suffered the injury in the third quarter Sunday when he scrambled to his right, attempted to slide, and was sandwiched between two Falcons defenders. He walked off the field and later headed to the locker room. He didn’t return.

Green, now 42, lacked the mobility that won Griffin the Heisman Trophy last year and propelled him to the No. 2 overall spot in this year’s draft. Running is a fundamental part of Griffin’s game and a prime reason why the Redskins traded four high draft picks to the St. Louis Rams to move up in the draft.

Asking him to abandon his instincts would dramatically alter the Redskins’ offense, reduce Griffin’s value and, according to longtime NFL coach Dick Vermeil, prove futile.

“If he can run, he will run. That’s all there is to it,” Vermeil said. “I don’t care what you do. If a guy can really run, he’s going to run, and he’s going to make some plays.”

Vermeil, now retired, added that the worst thing the team and Coach Mike Shanahan could do is overreact to Griffin’s concussion, despite the NFL’s recent priority on protecting players from head injuries.

Shanahan said Monday that Griffin showed no further symptoms after Sunday’s game, but whether Griffin plays in this week’s home game against the Minnesota Vikings will be decided later this week. The NFL now uses independent concussion consultants to evaluate and clear players for games. Even if Griffin is a full participant in this week’s practices, he will visit a concussion expert for an objective opinion and clearance to play against the Vikings.

Howard Derman, a neurologist and co-director of Houston’s Methodist Concussion Center, is the independent evaluator who examines Texans players after concussions. He said a “mild” concussion is a general term that usually means a player did not lose consciousness and, if appropriate recovery time is allowed — at least a few days without contact to the head — a player such as Griffin won’t necessarily be more susceptible to future brain injuries. Within the first days after a concussion, though, the brain remains vulnerable.

The Redskins wouldn’t reveal their post-concussion protocol when asked by The Post on Tuesday, instead deferring to the league, but Derman said there’s usually a “ramp-up” period during which activity is increased each day. The Texans, for instance, would administer at least one more ImPACT (Immediate Post-Concussion Assessment and Cognitive Testing) examination, comparing the results against those taken before the season and the one administered shortly after the injury, to measure brain function.

If test results are acceptable, the Texans would gradually re-introduce a player to full practice participation, likely on Thursday, and if he shows no lingering symptoms — headaches, dizziness or problems with memory or balance — he would be sent on Friday afternoon to the independent consultant for final clearance.

Griffin said after last Sunday’s game that he planned to play against the Vikings. Derman said it’s possible for a player to fake his way through parts of the post-concussion process, but the ImPACT tests and signs detected by an independent evaluator reveal true brain health. Most players, Derman said, know now that returning too early is irresponsible.

“They want to play,” Derman said, “but they also know that going back to play too early may be jeopardizing them.”

Regardless, Derman said Griffin’s position and size — he’s listed at 217 pounds — suggest Sunday won’t be the last time he’ll be at risk for a concussion.

“Clearly there’s going to be issues,” said Derman, adding that quarterbacks and linebackers are most prone to head injuries. “ . . . Just the way he plays, there’s a higher likelihood that he could have an injury like that.”

Vermeil said that’s something the Redskins and their fans will have to come to terms with. Griffin’s skills are dazzling and effective, but in the NFL they’re also dangerous. He said it would be wasted time to lecture Griffin on the benefits of sliding to avoid contact or remaining in the pocket longer. Those are lessons, the former coach said, that will come with experience.

Shanahan, Griffin’s own coach, already has been offering such advice, but agreed at his daily news briefing Monday that experience is the best teacher. “Any time you get a hit like that in the National Football League, at least in my experience, when the quarterback gets a big hit like he received, they slide a bit sooner,” he said. “In plays that come, they kind of protect themselves a little bit more.”

After watching tacklers slam Griffin in earlier games, the Redskins already are calling fewer designed runs for their elusive rookie star. Vermeil said he also might design an offensive game plan that calls for fewer quarterback runs, but otherwise the Redskins should embrace what they have in Griffin, regardless of the risks. Green, the former quarterback, agreed.

“To take the mobility part out of Robert’s game, doesn’t make any sense,” he said. “Because that’s why you drafted him.”

When Green missed the first half of the ’07 season with a severe concussion, he decided to pay little attention to future risks. He had suffered injuries before, and coaches teach players that worrying about getting hurt is the surest path to another injury. So Green put his concussion behind him. He said he returned with the same aggressiveness and willingness to scramble, even if something told him that another big hit might again send him to the sideline.

If Griffin indeed plays Sunday, Green said he would expect the rookie to play without anxiety.

“I would say I was more protective of myself as I progressed from that standpoint,” he said. “But was it like something in my head — like a fear of it? There absolutely wasn’t any fear of it.”