The suspension stems from an after-curfew party Sunday night that has become the focus of a sexual assault investigation in which no charges have been filed.
It is not clear what role Dennis played in the alleged incident, which occurred at an apartment in a complex that is located across the street from the Southern California campus and is used as training camp housing for the football team.
The police have not questioned Dennis, sources told the Los Angeles Daily News, and Carroll told the Los Angeles Times he didn't know of any of his players having talked to the police.
Asked how long the suspension would last, Carroll told the Daily News: "It's indefinite. That's a word you would use in this case. I haven't really labeled it."
Carroll declined to specify to reporters the reason for the suspension. However, a source told the Times that Carroll said in a team meeting that Dennis was suspended for breaking team rules that forbid drinking and having women in training camp dorm rooms.
Sources told the Daily News that the alleged victim arrived after an 11 p.m. curfew. According to the newspapers, the party was attended by fewer than 20 people, at least 14 of whom were associated with the football team.
Dennis, 20, played in every game last season, rushing for 661 yards and four touchdowns as part of a tailback rotation.