"Happy Gilmore" star Christopher McDonaldmay have been a bit over-served at the Bills game on Sunday ... 'cause he appeared to be very intoxicated -- stumbling and swaying while inside the stadium's concourse.
Check out this video obtained by TMZ Sports ... the actor -- who played Shooter McGavin in Adam Sandler's blockbuster golf flick -- looked like he could hardly stand during Buffalo's contest with the New York Giants at Highmark Stadium.
In the footage, which was taken at halftime of the game, McDonald can be seen nearly falling down some stairs ... before two men helped save him from a face plant.
He was also spotted in the clip needing some further assistance from the guys as he wobbled back to his seat -- all while several people yelled "Shooter!" at him.
One witness at the game tells us McDonald -- a diehard Bills supporter -- was then seen inside of a suite getting water from pals.