Charlie Sheen -- Even I'm Worried For Johnny Manziel

You know you've got some serious issues when even Charlie Sheen is scared for your well being ... and that's just the case for Johnny Manziel.

Sheen took to his Twitter account Saturday morning to offer some advice for the struggling QB, saying, "it's time 2 refocus all of your energy on health & Football! it's never 2 late 2 get a fresh start!"

As TMZ reported ... Dallas cops opened an investigation on Manziel Friday after claims by his former girlfriend saying he hit her during an argument.

So there ya have it Johnny, the MaSheen has spoken.