Mbakwe was arrested on July 1 and was sentenced to one year of probation and community service on Sept. 10. He missed almost all of last season with a knee injury and his return was expected to boost the Golden Gophers into contention in the Big Ten.
Smith reprimanded Mbakwe "internally" this offseason after the forward was charged with a DWI, according to a source close to the team. Mbakwe won't miss any games, the source said.
But Smith says Mbakwe was suspended from team activities after his arrest and "has got a lot to do to prove he's going to be able to contribute."
Smith says Mbakwe will start the season coming off the bench. He says he considered dismissing Mbakwe from the team before deciding to give him one more chance.
The source confirmed an earlier report that Mbakwe was convicted of driving while under the influence in September after a summer traffic stop.
"It's already been handled internally," the source told ESPN.com.
The source added that Mbakwe is practicing and won't miss any games this season because of the incident.
"It's something that happened earlier in the summertime," Mbakwe said. "Coach has been well aware of it. It's something that we're handling internally as a team and at this time I have nothing else to say about that."
Mbakwe declined to elaborate further on the incident, but did say he is looking forward to finally hitting the court again with a deep team that enters the season with high expectations. His knee is feeling great and he's been working out and is ready to roll.
"I'll definitely have those first-game jitters," Mbakwe said. "I'll definitely be excited and just ready to play again. It'll probably take me a little bit, but hopefully I'll be able to adapt pretty quick."
The Pioneer Press reported Mbakwe pled guilty to driving with a blood alcohol level above .08, a misdemeanor, in Minnetonka, Minn. He was sentenced to two days in a workhouse and 16 hours of community service last month, according to the publication.
Mbakwe missed the majority of last season after tearing his ACL in November. He was granted a sixth year of eligibility to compete during the 2012-13 season.
This is not Mbakwe's first encounter with the law.
He missed the 2009-10 season as he awaited trial on a felony-assault charge in Miami. Mbakwe maintained his innocence, and the case never went to trial.
Mbakwe entered a pretrial intervention program that promised him a clean record after he completed community service and made a small donation to a battered women's shelter. But Florida prosecutors threatened to reopen the case if Mbakwe failed to stay out of trouble.
Mbakwe led the Big Ten in rebounding the following year. But during that season, he was arrested after sending a Facebook message to a woman who had a restraining order against him. Mbakwe eventually pled guilty to misdemeanor violation of the restraining order.
Smith also knows the 23-year-old Mbakwe is relying on this season to prove he is fully healthy and take a shot at the NBA.
"I know he made a mistake and we'd come this far with him and he had a serious injury," Smith said. "One of the things is I think Trevor has the possibility of having a livelihood in this profession in pro basketball, so I wanted to make sure we gave him every opportunity, as long as he does the things we expect and require him to do."
Smith clearly was upset by the latest incident, going so far as to say that Mbakwe's status as a player the team can rely on is far from certain. The forward has a couple of weeks to get himself back in Smith's good graces before the games begin.
But he has some work to do.
"You're talking about a guy that played seven games last year," Smith said. "So he's got a lot to do to prove that he's going to be able to contribute."
Information from The Associated Press was used in this report.