McIntosh tore both the ACL and MCL in the first quarter of Sunday's 22-10 victory over the New York Giants. An MRI on Monday confirmed the diagnosis, and he will have reconstructive surgery in the coming weeks.
The rehabilitation time for a torn ACL is usually nine to 12 months.
"It's a real negative for us," coach Joe Gibbs said Monday. "He was playing great for us."
McIntosh, a second-year player from Miami, took over as the starting weakside linebacker this season. He has 87 tackles and three sacks.
Rookie H.B. Blades and veterans Randell Godfrey and Khary Campbell could all vie for playing time to fill McIntosh's spot over the final two games as the Redskins (7-7) make a push for the playoffs. Washington likely needs to win both games to make the postseason.
McIntosh is the second defensive starter to tear an ACL and MCL this season. Cornerback Carlos Rogers, who was hurt in the Oct. 28 game against New England, faces a difficult rehabilitation to return in time for the start of next season.
Also Monday, tight end Todd Yoder had an MRI on his right knee. The exam revealed a cartilage defect, but the Redskins hope he can play with it.
"We'll take it day-to-day and see how he does with it," trainer Bubba Tyer said.
Copyright 2007 by The Associated Press. All Rights Reserved