Casey Kulas of ESPN Cleveland ( @CaseyKulas ) noted on his Twitter that there he heard from sources at this past Monday's RAW in Cleveland that there was a heated exchange backstage between CM Punk and WWE staff.

According to Kulas, the clash had to do with Punk being diagnosed with a concussion. Punk was reportedly heard saying, "I passed all your damn concussion tests" and "I'm not going out and telling fans that BS."

Again, there are lots of stories going around as to why Punk left, so take this as a rumor for now.

@dajosc11 contributed to this article. Follow Raj Giri on Twitter at @RajGiri_303. Got a news tip or correction? Send it to us by clicking here.