Robbie Hummel doesn't have much of a poker face.

Purdue's star forward has missed the season with a torn anterior cruciate ligament in his right knee, reducing him to being a 6-foot-8 assistant coach. His frustration with that role was clearly visible as he watched No. 1 Ohio State dominate the visiting Boilermakers in an 87-64 win on Tuesday night.

"It's hard to watch guys you care about and that you're good friends with struggle through something like that," he said Wednesday. "It's never fun to get beat like that. Watching that from the bench is kind of a helpless feeling because you really can't do anything about it."

He's been there before. Hummel was second on the team with 15.7 points and 6.9 rebounds per game last season before a torn ACL in his right knee ended his season on Feb. 24. He had surgery, recovered and expected to play this season, but he reinjured the knee during practice Oct. 16 and had another surgery a month later.

Hummel said doctors have told him his recovery is about a month ahead of schedule, and his plans for returning next season are on track. Everything looked fine after the last surgery, too, but that hasn't prevented him from having a positive outlook.

"I've been optimistic about it," he said. "I'm really not doing anything different. It's really been the same. I really feel like last time was a fluke."

Hummel said the normal recovery time is six months, and he sees that as a legitimate goal. Purdue coach Matt Painter said all the signs he has seen are good.

"You can sit around and worry all you want," he said. "You have to push forward, and you have to support him."

The Boilermakers were ranked No. 3 in the nation before Hummel's season-ending injury last year, then they stumbled briefly without him before recovering to reach the round of 16 in the NCAA tournament. This season, the Boilermakers are 17-4 and ranked No. 12 without him.

"I think that we've played at a pretty high level for the last four or five games, not counting the Ohio State game," Hummel said.

Painter said Hummel has helped the young players and remains a key part of the team.

"When you're sitting over there and you're not playing, you can see things and pick up things, and it kind of comes from that coach's perspective," he said. "Any time Rob can talk to those guys and help them, it's a positive."

Hummel has not been cleared to jump yet. He has been focusing on strengthening his legs with low-weight, high-repetition lifting. He said swelling has not been a problem, and he said it is starting to feel normal.

Hummel doesn't appear injured to a casual observer — he can walk normally and said he feels normal. He said the problems would come if he tried to plant or quickly change direction.

"Last night, the student section thought I looked like I was fine and I should go in and play," he said. "I wish that was the case. My legs are still pretty weak right now because of the two surgeries and the not doing much. If I was to go in there right now, I'd be a shell of myself."