Griffin also likely tore at least part of his anterior cruciate ligament (ACL), but it's unknown how severe it is because a previous knee injury he suffered at Baylor in 2009 required two screws and a rubber band to hold it together.
Griffin is expected to undergo surgery this week on his torn LCL and at that time doctors will determine how much damage has been done to his ACL, a source told ESPN NFL Insider Adam Schefter.
Because of the previous injury, doctors initially could not determine Monday if his ACL was partially or completely torn and doctors don't know what surgery should be performed.
The Washington Post reported earlier that Griffin's MRI suggested partial tears to the ACL and LCL.
Griffin, who entered Sunday's wild-card playoff game already nursing a previously sprained LCL in the same knee, appeared to tweak the knee on a pass attempt in the first quarter and then left the game in the fourth quarter after twisting his leg while attempting to recover a muffed shotgun snap.
Redskins coach Mike Shanahan said in a news conference Monday the results of the MRI are prompting the team to send Griffin to Pensacola, Fla., on Tuesday to see orthopedist Dr. James Andrews, who serves as a Redskins' physician, for further examinations to determine how to proceed.
"There is a concern," Shanahan said. "That's why he's going to see him."
Andrews, meanwhile, tried to clarify comments he made Sunday to USA Today that he didn't clear Griffin to return to the Dec. 9 game in which he originally hurt his knee, as Shanahan had claimed the following day.
On Monday, Andrews told The Washington Post that "Shanahan didn't lie about it, and I didn't lie."
"I didn't get to examine (Griffin's knee) because he came out for one play, didn't let us look at him and on the next play, he ran through all the players and back out onto the field," he told the newspaper.
"Coach Shanahan looks at me like, 'Is he OK?' and I give him the 'Hi' sign as in, 'He's running around, so I guess he's OK.' But I didn't get to check him out until after the game. It was just a communication problem. Heat of battle. I didn't get to tell him I didn't get to examine the knee. Mike Shanahan would never have put him out there at risk just to win a game."
Information from The Associated Press and ESPN NFL Insider Adam Schefter was used in this report.