Rettig was injured during his collegiate debut in Saturday's 31-13 loss to Notre Dame. Eagles coach Frank Spaziani said Sunday that Rettig would be re-evaluated this week. Rettig did not practice Sunday and the team is off Monday.
Earlier Sunday, The Boston Globe reported that Rettig would miss at least a few weeks and perhaps the rest of the season.
Rettig limped off the field Saturday after he was hit in the pocket early in the second quarter and did not return. Rettig completed 5 of 10 passes for 72 yards before leaving the game, including a 58-yard touchdown.
"I'm pretty sure I was leaving the pocket and I did a spin move back," Rettig said after the game. "And I think a defender that was trailing me just slid into my ankle. It's tough to get in the game and have things start flowing and then you get pulled out. That's disappointing and hard to swallow."
Rettig's replacement, sophomore Mike Marscovetra, completed 22 of 37 passes for 193 yards -- all career highs -- but threw a pair of interceptions.
Dave Shinskie started the first three games of the season, but he lost his job after last week's 19-0 loss to Virginia Tech.
Information from The Associated Press was used in this report.