Kyle Shanahan has insisted that Cleveland Browns quarterback Jonny Manziel is a "great guy", despite criticism of his behaviour.

The 22-year-old earned a reputation through his college days of a partying lifestyle, which carried over into his first year with the Browns after being selected in the first round of the 2014 Draft.

However, Shanahan, who served as Manziel's offensive coordinator at the Browns last season, is adamant that he was a hard worker and a good person to be around.

"Johnny's a great guy and I think he does get a little bit of a bad rep with that, because Johnny worked very hard for me," Shanahan told reporters. "I really enjoyed coaching him.

"I don't know what he's going through, but I think I'm confident Johnny will work it all out. And I think he has a chance to have a good future."

Manziel entered rehab last week to seek treatment for personal problems.