There are reports that White ruptured his Achilles. The Broncos have had a rash of injuries at RB with Moreno and Buckhalter both missing extended periods. White wasn't going to be the Broncos leading rusher this year, but they were counting on him as a veteran backup/short yardage back.
Every team has injuries, it's when the injuries happen at one position that it becomes a real problem. The Broncos could have issues with RB depth all year.