The 7-footer underwent an MRI on Tuesday, and the team provided a medical update before Wednesday's game.
The Cavs said Mobley, one of the front-runners for Rookie of the Year, will not travel with them on an upcoming trip this week to Atlanta and New York. Cleveland will be back home Sunday to host Philadelphia.
There is no timetable on when Mobley will be back, but head coach J.B. Bickerstaff said Mobley is not in a walking boot, perhaps an encouraging sign the injury isn't long-term.
Saddled with injuries all season, the Cavs are currently in the No. 7 spot in the Eastern Conference. The top six teams have guaranteed playoff spots while teams 7-10 will participate in a play-in tournament.
Mobley's injury also comes while the Cavs are playing without All-Star center Jarrett Allen. He has missed 12 games with a broken finger, and it's not known if he'll be back during the regular season.
The third pick in this year's draft, Mobley is averaging 14.9 points, 8.3 rebounds, 2.5 assists and 1.6 blocks. The 20-year old is one of the main reasons behind Cleveland's turnaround season. The Cavs are 42-34 after winning just 22 games a year ago.
The Associated Press contributed to this report.