Houston's Michael Brantley tipped Nestor Cortes' 92 mph fastball straight back into Muchlinski on the second pitch of the game on a hot, sunny day in the Bronx. Muchlinski staggered and was grabbed by catcher Jose Trevino, who helped the umpire steady himself.
Muchlinski held on to Trevino while he consulted with a trainer and the rest of the umpiring crew but remained in the game.
Muchlinski met again with a trainer after the top of the third inning. He was escorted off the field, and the game was delayed while crew chief and second base umpire Todd Tichenor suited up to take over behind the plate.
The 45-year-old Muchlinski has been working in the majors since 2006.