49ers Players -- We'll Miss Harbaugh ... He'll Crush It At Michigan!

Jim Harbaugh had a strong fan base in own locker room ... with a bunch of S.F. 49ers players telling TMZ Sports they loved their former coach ... and explaining why he'll be sorely missed.

Carlos Hyde (RB), Marcus Cromartie (DB), Marcus Martin (C) and Kenneth Acker (CB) were all out at The Grove in L.A for lunch ... when we asked if there were any hard feeling toward Harbaugh, who just left S.F. for the top job at the University of Michigan.

"Harbaugh was a good coach," Cromartie said.

Martin agreed ... saying, "We was thankful for Coach Harbaugh. He did a lot of good things for us."

But the best part of the video ... check out their reaction when we ask how they feel about Johnny Manziel.