Marra was pivoting and trying to make a pass early in practice when he was injured, coach Rick Pitino said in a statement.
An MRI is scheduled for Saturday, but Pitino told WHAS 840-AM radio in Louisville that Marra re-tore his ACL. It's the same injury that sidelined Marra for all but two games during the Cardinals' run to the Final Four last season.
"An unfortunate thing happened today," Pitino told the radio station. "We've been working Mike Marra out individually for the past two months and he'd passed all the tests. Literally in the first 10 minutes of practice, he blew out the same knee with an ACL."
The injury continues a run of bad luck for both Marra and Louisville.
Last season, the Cardinals overcame a rash of injuries to reach the Final Four. Along with Marra, Rakeem Buckles (ACL) and Stephan Van Treese (patellar) missed the entire year. Wayne Blackshear (shoulder), Peyton Siva (concussion/sprained ankle), Kyle Kuric (sprained ankle) and Jared Swopshire (groin) all missed significant playing time.
With a hefty roster of returning players, the Cards likely will rank in the top five in most preseason polls. Losing Marra won't change that, but it is still a significant loss for a team just three weeks before practice starts. Marra is a solid outside shooter, something Louisville's ineffective offense needed desperately a year ago.
Pitino told WHAS that he intends to keep Marra involved with the program this year, moving him from the court to the bench.
"Mike wants to be a coach," he said. "I just told him, 'Mike, after all these injuries, you're not going to be a professional basketball player, but you're going to get a year's head start on being a graduate assistant to a top-10 team. You've got to look at the positive.' This will give him an opportunity, like my son Richard at Providence who became a GA as a senior, to get a head start on his coaching career."