Coach Lindy Ruff provided the update Saturday, a day after Gragnani was hurt in a rookie scrimmage. Ruff didn't say which knee suffered the Grade 2 sprain, but noted it won't require surgery.
"He came into camp in real good shape and he's pretty disappointed," Ruff said. "He realizes it's a missed opportunity to play some games and show skills. We're disappointed but obviously there will be another chance for him."
Gragnani, the Sabres' third-round pick in the 2005 draft, was expected to compete for a regular job with the team this season. He's previously appeared in six career games with Buffalo, but has yet to score a point.
Forward Mark Parrish, an 11-year NHL veteran, joined the Sabres in opening training camp on a tryout basis.
A six-time 20-goal-scorer, he had two assists in 16 games with Tampa Bay last season.
Information from The Associated Press was used in this report.