Shannon Sharpe -- BLASTS MANZIEL ... Image Makeover Is a Crock (VIDEO)

Shannon Sharpe says Johnny Manziel's attempt to change his image is a bunch of BS -- claiming he's sick of people believing all of the crap Manziel has been trying to feed the public for years.

The NFL Hall of Famer was out in L.A. when we asked about the statement Manziel issued Tuesday night ... in which he finally acknowledged he has "issues" and vowed to get back in the NFL.

Long story short ... Sharpe ain't buyin' it.

"How long are you gonna buy his story?" Sharpe asked ... "He's shown no remorse, he's shown no willingness to change his behavior ... but you believe it and that's the problem."