Surgery to repair two ligaments in the right knee of Washington Redskins quarterback Robert Griffin III was completed just after noon Wednesday, according to a person familiar with the situation.

Dr. James Andrews repaired Griffin’s lateral collateral and anterior cruciate ligaments, in a procedure that began about 7 a.m., the person said. According to that person, Griffin plans to remain in Florida for the foreseeable future to be monitored and begin his rehabilitation. The initial six to eight weeks of recovery are considered critical key to his rehabilitation, the person said.

Experts said Griffin could face a lengthy rehabilitation that might jeopardize his chances of being ready for the start of the 2013 season in September and could keep him sidelined even longer.

The Redskins haven’t responded to requests for information on the surgery or the condition of Griffin’s knee, which was determined when he was examined by Andrews in Gulf Breeze, Fla., on Tuesday. The people who discussed Griffin’s situation spoke on the condition of anonymity because they were not authorized to talk about the matter publicly.

Mark Adickes, the orthopedist who performed Griffin’s original ACL surgery in 2009, declined to comment. He said he is consulting with the Griffin family and physicians at this time.

Washington Post columnist Jason Reid talks about his conversation with Redskins Coach Mike Shanahan and describes why he thinks Shanahan should have benched Robert Griffin III in the Redskins’ loss to the Seahawks. (The Washington Post)

Early Wednesday, the following message was posted on Griffin’s Twitter account: “Thank you for your prayers and support. I love God, my family, my team, the fans, & I love this game. See you guys next season.”

Griffin was examined Tuesday outside Pensacola, Fla., by Andrews, an orthopedic surgeon. The Washington Post reported Monday that an initial MRI exam of Griffin’s knee showed possible tears of the two ligaments. Coach Mike Shanahan said at a news conference Monday that the test was inconclusive and that Griffin would see Andrews to determine whether those results reflected new injuries or previous ones.

James C. Dreese, a doctor for University of Maryland athletic teams, said an LCL tear requires a longer rehabilitation process than an ACL tear. Dreese, who has no specific knowledge of Griffin’s injury, said an LCL tear could keep Griffin out for eight to 12 months.

The length of the rehabilitation depends on whether the ligament can be repaired surgically or requires a more extensive reconstruction using a graft from another part of the body or a cadaver. A torn ACL typically requires a six- to eight-month rehabilitation.

“When the collateral ligaments are involved,” Dreese said, “the concern in the long term is that controlling the rotational component of the knee can be more difficult.”

Dreese also said LCL tears are usually accompanied by injuries to one of the cruciate ligaments — the ACL or PCL (posterior cruciate ligament). However, he said if there is an ACL tear in addition to the LCL tear, it would not necessarily lengthen Griffin’s rehab.

Several people with knowledge of the case said Monday that the MRI of Griffin’s knee showed he might have suffered at least partial tears of his ACL and LCL.

Ligaments work to allow the knee to bend forward while limiting its ability to rotate and flex side-to-side. On the play in which Robert Griffin III was hurt, the lower half of his knee makes both of those movements to excess, suggesting an injury to the anterior cruciate ligament.

Team officials refused to comment Tuesday about the results of Andrews’s exam and the extent of the damage to Griffin’s knee.

Griffin tore the ACL in the same knee in 2009, when he was a sophomore at Baylor University.

Tim Kremchek, medical director and chief orthopedic surgeon of the Cincinnati Reds, also said that a full-scale LCL tear could be more devastating than a torn ACL. Unlike the ACL, the LCL cannot be surgically repaired with an arthroscopic operation, he said.

“It could be worse,” Kremchek said Monday, before word of Griffin’s condition emerged. “It depends on how much is done. It’s a big, open incision. The rehabilitation is slowed down. It’s not as quick to make the muscles strong. It’s dicey. The outside ligaments are a worse problem. They’re not as predictable as an ACL.”

Minnesota running back Adrian Peterson, who tore his ACL on Dec. 24, 2011, in a game against the Redskins at FedEx Field, defied the odds and returned to action by the start of the 2012 season. He played in all 16 games, finishing nine yards shy of the NFL’s single-season rushing record.

Griffin initially sprained the LCL four weeks ago when he was hit in a win over the Baltimore Ravens. He appeared to re-injure it in the first quarter of the Redskins’ 24-14 playoff loss to the Seattle Seahawks on Sunday. He remained in the game until the fourth quarter, when his knee buckled awkwardly and he could not continue.

Since then, controversy has swirled throughout professional football over whether Shanahan should have pulled his star rookie from the game, despite Griffin’s insistence on continuing to play even as his mobility appeared to diminish.

DeMaurice Smith, executive director of the NFL Players Association, said Tuesday that the union is looking into the Redskins’ handling of the quarterback’s injury. Smith said the union also is looking into the condition of the playing surface at FedEx Field during Sunday’s game, which was criticized by, among others, Seattle Coach Pete Carroll.

Griffin and team owner Daniel Snyder arrived at the Andrews Institute for Orthopaedics and Sports Medicine in Gulf Breeze, Fla., on Tuesday. The appointment was believed to have lasted just more than two hours, according to a person with knowledge of the situation. But it wasn’t clear what kinds of tests were conducted.

The Redskins have said they will make a formal announcement about Griffin’s injury “at the appropriate time,” and when there is a definitive diagnosis.

On Dec. 10, a day after the Baltimore game, Shanahan announced that MRI exam findings revealed that “Robert has a mild strain of the LCL. It’s Grade 1. He’s had some mild swelling. He had his right knee repaired — his ACL — in 2009. That looks great. No problem there.”

In the first quarter Sunday, however, Griffin came up hobbling badly after rolling to his right, planting on the injured right leg and throwing an incomplete pass. Griffin limped back to the huddle and two plays later threw a touchdown pass, but his mobility decreased significantly over the next 21 / 2 quarters.

Midway through the fourth quarter, one play after he was sacked for a 12-yard loss, Griffin’s knee bent awkwardly as he scrambled for a loose ball. Team trainers and Andrews, who is on the sideline for every Redskins game, tended to him. Griffin was helped up, limped off the field and did not return.

Adam Kilgore contributed to this report.