He fell onto his shoulder while diving for a ball in a non-contact drill.
Rubin is expected to be out approximately four weeks. No surgery is required.
The four-week rehab period means Rubin will likely miss at least the first two games of the season, a Sept. 2 home matchup with Akron and a Sept. 9 trip to Notre Dame.
Though Penn State must replace all four starters in the secondary this year, there is plenty of talent at the safety spots even without Rubin. Donnie Johnson, Spencer Ridenhour, Nolan McCready, Anthony Scirrotto and Darien Hardy were all lauded for their play at the positions in the spring.
Rubin played wideout as a true freshman in 2004, making 16 catches for 187 yards. While redshirting last season, he was stationed at safety in practices leading up to the Orange Bowl. He remained at the position in the spring.