"Yadi tightened up a little bit." Matheny said. "I don't know if it was a cold or what it was exactly, so we'll have to keep an eye on him."
Molina missed 40 games last season after thumb surgery and 16 games in 2013 with a pair of knee issues, but has never missed significant time due to back or shoulder injuries.
The veteran catcher has been uneven at the plate this season, batting .276/.325/.343 through 115 plate appearances without any home runs.
August Fagerstrom is an associate reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.