The Post's Jason Reid says after last night's loss to the Broncos, the Redskins need a win against the Chargers on Sunday if they want to do well this season. (Sarah Parnass/The Washington Post)

For a short while, the worry was back — even in the mind of the second-year quarterback with the 335-pound defensive tackle lying on him.

Robert Griffin III, the Washington Redskins’ franchise player who damaged two ligaments in his right knee this past January, fell to the ground again in the fourth quarter Sunday. He grabbed at his left knee after Denver Broncos lineman Terrance Knighton drove him into the turf — and Washington’s fan base held its breath.

“I think it really just scared me,” Griffin said.

He said the team’s medical staff cleared him to return to Sunday’s game, a 45-21 Washington loss, but Coach Mike Shanahan opted to end Griffin’s afternoon with a little more than four minutes to play.

“There was no point in risking anything at that point,” said Griffin, who even before the injury had perhaps his worst passing day as a pro. He completed half of his 30 passes, was responsible for three turnovers, and finished with a career-low 45.4 passer rating. He now has eight interceptions in seven starts, three more picks than he threw in 15 games in 2012.

Backup Kirk Cousins didn’t perform much better in relief, throwing an interception on his first series and chasing Broncos cornerback Dominique Rodgers-Cromartie as he returned the pick 75 yards for a touchdown.

“I thought I could fit it in,” Cousins said, “but clearly [Cromartie] was baiting me.”

Still, the attention at the time remained on Griffin, who despite starting each of Washington’s games this season, hasn’t made a definitive case that he has full confidence in his right knee. He suffered the injury — which required his second ligament-replacement surgery in four years — in a playoff loss to Seattle nearly 10 months ago. He vowed to return in time to start the season opener, and although he made good on that, he hasn’t yet shown the breakaway speed, confident footwork, and finely tuned mechanics that earned him rookie-of-the-year honors in 2012.

All of which has done little to ease worries that Griffin’s 6-foot-2, 217-pound frame could be suspect to future injuries. So when Knighton forced Griffin to the ground, forcing an interception and turning his left leg awkwardly before he fell, it was natural to wonder if this was just the next one.

Maybe Griffin himself wondered that.

“Those two or three seconds,” he said later, “when you have a 300-plus pound guy laying on your leg, it’s going to scare you a little bit.”

He said the knee was fine and would require no further testing to determine whether there was additional damage. As he left the field following handshakes with Denver players, he walked with no noticeable limp, and shortly afterward in the locker room, his leg wasn’t wrapped or braced.

“I think he’s okay,” Shanahan said, surely a relief not only because his team needs its starting quarterback but because of the criticism he shouldered throughout the offseason.

Shanahan took on heavy fire during the months following Griffin’s knee injury last January. Should he have removed his starter, who was clearly hobbled even before a fourth-quarter play in which he chased a bad snap and crumbled to the turf? Should he have played at all after an earlier, less severe knee injury four weeks earlier? Should Shanahan and his son, offensive coordinator Kyle Shanahan, design game plans with fewer running plays, exposing Griffin to increased hits?

The coach seemed willing to take no such chances Sunday, and Griffin offered no second-guessing following the decision.

“It was just smart to keep me off the field,” he said, “and just be ready to go next week.”

He acknowledged that Washington’s offense needed to improve, saying he couldn’t believe his team was 2-5. Griffin added that he was among those who must “do more,” and he asserted that such improvement would happen. At least now he’ll get the chance to continue working, despite Sunday’s scare.

“Everybody in that locker room has to be better,” he said, “and we will.”