BATON ROUGE, La. -- LSU's dismissal of 2011 Heisman Trophy finalist Tyrann Mathieu from its football program on Friday came after the cornerback's repeated violations of LSU's substance abuse policy for athletes, a source with knowledge of the situation told ESPN.com.
Mathieu was suspended for a game last year for failing a drug test, and he had been undergoing counseling throughout the spring and summer, the source said.
At a news conference on Friday, LSU coach Les Miles said Mathieu's dismissal was for a violation of team rules.
Miles confirmed it was not a legal issue. "Both," he said when asked if the dismissal was because of a team rule or a school rule.
"We extended ourselves personally and professionally to him," Miles said. "He has really improved and has a chance to take some steps as a person. ...
"I complied and agreed that it was right," Miles said. "We'll miss the guy. The football team's got to go on. We'll have to fill the void."
A source told ESPN's Joe Schad on Friday that Mathieu has been looking for a new school to play for this season. Mathieu has two years of eligibility left and could transfer, but he would have to sit out this season if he went to another school in major college football. If he moved down a level, to FCS, he could play right away.
"I can't imagine he would be here and not want to transfer and go play football," Miles said. "We will help him in every way we can."
Last season Mathieu, who is nicknamed Honey Badger, was a surprise finalist for the Heisman and won the Chuck Bednarik Award as the nation's best defensive player.
The junior defensive back helped the Tigers win the SEC championship and reach the BCS title game. LSU lost the championship 21-0 to Alabama.
LSU enters this season ranked No. 1 in the USA Today coaches' poll. The AP college football poll will be released Aug. 18. The Tigers opened preseason camp last week as one of the favorites to reach the national championship game again. LSU started closing practices on Wednesday, but officials said Mathieu practiced at every practice until Friday morning, when he was informed of his dismissal.
"I called on the leadership of this team to understand that these things happen and they certainly understand it and they are ready to take positive steps," Miles said of the decision, which officials said was made Thursday night.
Mathieu was the team's big-play machine at cornerback and on special teams. The All-American scored four touchdowns -- two on punt returns and two on fumble returns -- intercepted two passes and caused six fumbles and recovered four last season.
"At the time, I think it's an opportunity to redirect and I think he still has a bright future," Miles said. "He can still accomplish all the goals he set for himself. It's not going to be easy, but it's going to be doable.
"For the team, we lost a quality person. We enjoyed working him. He was a great teammate.
"I think he gave us a lot of examples we can learn from. I think he is a quality, quality guy who had a behavior issue. That's it. Certainly the overview of his time with us is positive."
LSU athletic director Joe Alleva said Mathieu's rule violations were an "ongoing issue."
"This was just a team policy, not going to confirm or deny either way, " Alleva said when asked if the dismissal was related to last year's one-game drug suspension.
"The policy is a written policy. It's like the speed limit, if you are going over the speed limit, you're breaking the law. He's been over the speed limit. As in, he's been over it a lot."
Asked if it was a legal issue, as in a law violation, or just policy, Alleva said, "policy," and added that LSU made efforts to counsel Mathieu.
"We do everything we can to help these kids. He's had help and we've been trying to help him all along in everything," Alleva said. "Being an athlete is a privilege. You have to follow the rules to take advantage of that privilege and unfortunately, he doesn't have that privilege here any more. He's a good kid. He really is a good kid, it's a shame. But I told him this morning, that he has the rest of his life. His life is still ahead of him. He still has an opportunity to do good things."
Mathieu could stay at LSU and pay tuition, but Alleva said that was unrealistic.
"He's not going to stay in school," he said.
Mathieu has two years of eligibility left and could transfer, but he would have to sit out this season if he went to another school in major college football. If he moved down a level, to FCS, he could play right away.
The Tigers are No. 1 in the coaches' preseason poll. The AP college football poll will be released Aug. 18.
The Tigers open the season at home Sept. 1 against North Texas. Their only big nonconference test comes the next week when Washington and star quarterback Keith Price visit Tiger Stadium. LSU opens SEC play on the road Sept. 22 at Auburn and renews its rivalry with Alabama on Nov. 3 in Death Valley.
"I can't imagine he would be here and not want to transfer and go play football," Miles said. "We will help him in every way we can."
LSU isn't quite as deep at cornerback as it was last season, when it had All-American Morris Claiborne and often used Mathieu as a nickleback. Tharold Simon is the other expected starter opposite Mathieu. Second on the depth chart are redshirt freshman Jalen Collins and freshman Jalen Mills.
"We have good players," Miles said of potential replacements. "It's interesting. Eric Reid, Tharold Simon and a guy who's no longer on this team (Mathieu) all played very significant roles in a Cotton Bowl victory at the end of the season. We have similar type guys. The challenge will be to them."
Because of injuries, Reid, Simon and Mathieu all played a lot of snaps in the 2011 Cotton Bowl as true freshmen. This suggests that true freshmen will have to play a lot.
"I think (sophomore) Odell Beckham is a very talented punt returner and I think we're good at kick returner as well," Miles said.
Information from ESPN.com's Chris Low and The Associated Press contributed to this report.