Ndamukong Suh's Teammates -- Celeb Diving Show is a HUGE MISTAKE!

Ndamukong Suh should NEVER have signed up to compete on "Celebrity Diving" ... this according to several of Suh's Detroit Lions teammates who tell TMZ the decision is shockingly irresponsible.

We broke the story ... Suh -- who's in the middle of a 5-year $68 MILLION contract with the Lions -- recently joined the cast of the ABC reality show ... and will be required to launch his 6'4", 307-pound body off a high diving board.

TMZ spoke to a BUNCH of Suh's teammates ... who all feel (very strongly) that he's making a huge mistake.

One source tells us ... "We need him on the field and if he gets hurt during the off-season doing wild stunts ... it would be bad and it ain't worth it. He is too valuable to the team."

Another source expressed similar concerns -- "if he gets a busted ear drum or an infection, it could have serious effects on his off-season training."

Several of Suh's teammates also told us they were surprised the organization would allow him to participate in the first place ... since there is a real serious risk he could hurt himself.