"I think that for my safety and my future -- I'm not going to the NFL -- I need my brain," Diamont told reporters Saturday. "So that was the decision."
The junior participated in senior day activities at Memorial Stadium. He said he has endured "a lot" of concussions in his career.
"I think some of those hits are adding up on him," coach Kevin Wilson said.
Purdue's final chance ended when the Hoosiers' Jonathan Crawford hauled in the first lateral on the ensuing free kick.
Diamont finished with 42 rushing yards and a touchdown on 13 carries Saturday. He was 0-for-3 passing.
The Associated Press contributed to this report.