The game at Citi Field on Monday night was delayed for 11 minutes.
Foster was struck squarely on the mask by a ball off the bat of Toronto's Josh Donaldson with one out in the top of the third inning. Foster kept feeling his jaw and moving his mouth while being checked by a Mets trainer for several minutes near home plate.
Foster then remained in the game for two more batters but did not come out for the bottom of the third. Crew chief Mike Winters, who was working at second base, took over at home.
The game continued with three umpires.