Johnson feels that there is no harm in the 21-year-old's behaviour as long as he puts the work in when the time comes to concentrate on football.
"Be your own man," Johnson told NJ.com. "Do what you got to do. It's the off-season. That's when you get time to do whatever you want to do and live your life.
"I'm pretty sure once the season gets here, he'll be all right. He's going to focus in on football. But this is the time now to where he'll be able to hang out and do some of the things you want to do.
"Because once the season gets here, you really have no life. It's just football and football."
Manziel was selected 22nd overall by the Browns in the 2014 Draft.