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.