Eric Dickerson says if Jeff Fisher thinks he left the Rams in good shape when he was fired he's DEAD WRONG ... telling TMZ Sports the team was in shambles when Fisher exited Hollywood.

Fisher has recently done a little self-back-patting over the Rams' current success, saying in a recent interview he feels at least partly responsible for the team's unbelievable turnaround.

ED thinks this is total BS -- and told us as much during the So. Cal Rams Booster Club event at Rocco's Tavern in Studio City ... essentially explaining why Fisher needs a reality check.

"Do I think he left the team in a good spot,? No I do not. Personally I don't. I don't think he helped Jared Goff at all, I don't think he helped Todd Gurley at all. I don't think he helped the offense at all."