Johnny Manziel hasn't played a snap of football since he was placed in concussion protocol a month ago ... but Eric Dickerson says the CFL QB needs to trust the process and "don't rush back" to the field.
TMZ Sports spoke with the L.A. Rams legend -- who says he's a fan of Johnny's and even golfed with him in the past -- about the Heisman winner getting sidelined after a vicious hit he took in a 24-17 loss to Ottawa on August 11.
"A concussion is serious. They take it more serious these days than when we played," Dickerson says.
Johnny vocalized his frustration to reporters on Thursday ... saying he feels like he's ready to get back on the field, but wonders if the team still believes in him.
"If the club had faith in me, I feel like I would be the guy ... I feel like I would've been the guy after I came back from the concussion,'' Johnny said.
"That hasn't happened. So, I need to continue to get out here. And, it's the hardest part about missing practice, I need these reps to try to leave as little doubt as possible in my ability to play.''
But, E.D. warns Johnny to not get too eager to play just yet ... "My advice is don't rush back. There's a lot of football to be played.