Ricky Williams -- I Was Like Johnny Manziel ... It's Important for Him to Have Fun

Ricky Williams says Johnny Manziel has worked too damn hard to NOT go out and enjoy himself ... telling TMZ Sports, "Sometimes people need to have fun to play well."

Williams was in L.A. to tape a commercial for the ESPN Heisman House ... where he met Johnny Football for the very first time ... and says they got along great.

Of course, we had to ask Ricky about Johnny's penchant for partying -- and the ex-NFL star told us he not only approves, but says it could be imperative to his long-term success.

"You know, I was a rookie at one time, 1st round draft pick, and had a chance to do all the cool stuff I always wanted to do ... so I'm happy for him."

There's more ... Ricky also told us he's been doing "healing work" with ex-football players who suffer from concussion-related medical issues ... and has reached out to several former NFL stars to try to help 'em out.