The 25-year-old right-hander sustained a bruise on his forearm, but no fractures. He figures to be ready to make his next start -- given that start isn't scheduled until next season anyway.
Rangers third baseman Michael Young's hard shot off his right forearm ended Hernandez's final start of 2011 prematurely, his 3 1/3 innings the shortest outing of his season.
"He's OK. It'll be fine once he gets a little time," manager Eric Wedge said. "It's not broken, so that's the most important thing."
The Mariners were still without utility infielder Luis Rodriguez on Sunday, a gash on his right hand still healing after getting spiked on Thursday in Minnesota. That left rookie Kyle Seager as the only available shortstop for the third straight day, with starter Brendan Ryan back home in Seattle and likely done for the season with a sore neck.
"I was hoping to get Luis back in there, but he's still a day away probably," said Wedge.
The Mariners did get Justin Smoak back in the lineup Sunday at first base after four games of being limited to designated-hitter duties as he was coming back from a strained groin muscle.