Michigan safety Jordan Kovacs is third on the Michigan defense with 42 tackles this season.

Melanie Maxwell | AnnArbor.com

Michigan junior safety Jordan Kovacs is not on the dress list and will not play Saturday against Purdue.

A school spokesman said Kovacs suffered a knee injury and has not practiced since. A source told AnnArbor.com that Kovacs is questionable for the Iowa game as well because of the injury.

Kovacs' injury is a significant blow to the No. 17 Wolverines (6-1, 2-1), who take on upstart Purdue (4-3, 2-1) at noon Saturday on ESPN2. He had started all seven games this year and recorded 42 tackles, third most on the team.

He also had an interception and a team-high three sacks, despite playing safety.

Senior cornerback Troy Woolfolk is expected to start for Kovacs, who had been in the lineup for 28 consecutive games. He has never missed a game since becoming a starter midway through the 2009 season.

Freshman Blake Countess will start for Woolfolk at corner.

Backup safety Marvin Robinson, who has missed the past two games due to an undisclosed injury, also is expected to return, bolstering the depth at safety.

A source said junior safety Matt Cavanaugh wore Kovacs' No. 32 jersey at the team's practice Tuesday, which was available to the media. It is unclear if that was done explicitly to avoid drawing attention to Kovacs' injury, or if it was for scout team purposes.

Purdue starting safety Albert Evans also wears No. 32.

Kyle Meinke covers Michigan football for AnnArbor.com. He can be reached at 734-623-2588, by email at kylemeinke@annarbor.com and followed on Twitter @kmeinke.