Losing interior lineman Ondre Pipkins for the season is a tough blow for a Michigan defense coach Brady Hoke feels still has room to improve.
The potential return of All-Big Ten linebacker Jake Ryan may help it reach the level Hoke expects.
The 18th-ranked Wolverines look to remain unbeaten Saturday as they visit a Penn State team also searching for some consistency on the defensive side of the ball.
Pipkins suffered a torn ACL in Michigan's 42-13 win against Minnesota last week.
Michigan (5-0, 1-0) held the Gophers to 281 yards and ranks 13th in the nation in total defense, allowing 305.0 yards per game, but opponents are converting 41.1 percent on third down - 78th in the country - after Minnesota went 8 of 15.
"Getting off the field is important, and we've got to do a better job," Hoke said. "We've got to do a better job when you look at lanes and those kinds of fundamentals that you need to have. This defense is coming around. Is it exactly where we need it to be? No."
The return of Ryan, who led the team in tackles (88), tackles for loss (16) and sacks (4 1/2) last season, may provide a boost. Ryan had knee surgery after suffering an injury during a spring practice in March and has been cleared by doctors.
Hoke said he would like to see how Ryan responds in practice this week before making a decision on his status for Saturday.
"Believe me, he's wanting to play, and he seems to be feeling okay," Hoke said. "We need to make sure he can do the things he's capable of doing."
With or without Ryan, the Wolverines will be tasked with slowing a Penn State offense that has averaged 475.5 yards over its last four contests. Christian Hackenberg went 30 of 55 for 340 yards and three touchdowns while Allen Robinson had a career-best 12 catches for 173 yards and two scores last week, but the Nittany Lions (3-2, 0-1) fell 44-24 at Indiana.
"They are a physical football team," Hoke said. "It got a little crazy last weekend in Indiana - there were a lot of points and a lot of yards by both teams - but I think they are a very good football team."
Penn State coach Bill O'Brien didn't want to talk much about last week's contest that saw his inconsistent defense allow 486 total yards. It gave up 183 yards in a 45-7 win over Eastern Michigan on Sept. 7 and 190 in a 34-0 victory over Kent State on Sept. 21, but also allowed 507 yards in a 34-31 loss to Central Florida on Sept. 14 before last week's lackluster effort.
O'Brien is hoping his team can turn the page quickly.
"I think our identity is we're a tough team," O'Brien said. "We're going to play hard, and we've got a lot of good players, and we're very focused on doing that against Michigan."
The Nittany Lions will face a tough challenge in trying to contain Michigan quarterback Devin Gardner, who poses a threat through the air and on the ground.
Gardner has thrown eight touchdown passes while running for six, and his average of 63.6 rushing yards per game is tied for eighth in the nation among QBs. O'Brien's focus may be to force Michigan to throw more, as Gardner's eight interceptions are the most in the Big Ten.
The Wolverines' 16 rushing touchdowns are tied for second-most in the conference.
"He's a dangerous guy because he can run and throw, and there's a number of guys like that in this conference," O'Brien said. "I think the thing you've got to try to do is really try to keep him in the pocket. When he gets out of the pocket, he's very dangerous."
Penn State has won the last three meetings after dropping the previous nine, including a 41-31 victory Oct. 30, 2010, in the most recent matchup.