Ex-Detroit Lions Player -- Suspected HIT MAN in Murder-for-Hire Plot

A former Detroit Lions football player is suspected of being the hit man in a real-life Hollywood murder for-hire-plot ... law enforcement sources tell TMZ Sports.

The identity of the former NFL player has not been released ... but sources tell us the guy is VERY big (in size).

Here's the backstory -- we know ... celebrity skin specialist Dawn DaLuise was arrested Wednesday for allegedly trying to hire someone to kill a skin care competitor. Sources tell us the person she contacted once played for the Lions.

FYI -- The murder was never carried out ... cops stepped in after someone tipped them off about the alleged plot.