Simmons was covering after Seattle's Logan Morrison grounded an RBI single into left field. When Simmons hit the bag, his ankle buckled awkwardly and he crumpled to the ground while Justin Upton airmailed the throw over the head of catcher Gerald Laird.
Simmons limped off the field and was replaced by Ramiro Pena.
"He's probably going to be a little sore tomorrow," manager Fredi Gonzalez said. "Maybe the off-day on Thursday will give him plenty of time for this weekend."
Adam Lewis is an associate reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.