The Mariners said a precautionary X-ray of his right forearm was negative.
Hernandez was listed as day-to-day. He will be re-evaluated Tuesday.
The 31-year-old star, slowed by injuries last year, was struck by a liner from Victor Caratini of the Chicago Cubs.
After being hit, Hernandez immediately grabbed his arm and didn't pursue the ball on the infield grass.
Hernandez went down to a knee, hopped up and walked around in obvious pain. He headed to the dugout with a trainer holding his arm, and Caratini gave him a tap of encouragement.
Hernandez spent considerable time on the disabled list last season because of shoulder trouble. The 2010 AL Cy Young Award winner was 6-5 with a 4.36 ERA in 16 starts.
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