Here’s a report on the injury from PFT:
According to multiple reporters on the scene, Delmas was in coverage during the Dolphins’ joint practice with the Panthers when he went down and grabbed his right knee. Delmas tore his right ACL last year.
When healthy, Delmas is a very good safety. But he has struggled to stay healthy. The Lions cut Delmas after the 2013 season because they questioned whether he’d be able to stay health, and although he got off to a good start with the Dolphins last year, his torn ACL seemed to justify the Lions’ decision.