The Mariners announced that X-rays were negative and said Paxton has a bruised left forearm.
Manager Scott Servais and a team trainer rushed from the dugout to check on Paxton.
Paxton is 10-5 with a 3.68 ERA this season. He entered the day 11th among qualified starters with 3.6 wins above replacement, per Fangraphs.
Hernandez quickly began warming up to make his first career relief appearance following 398 starts. The 32-year-old was removed from the rotation last week amid a season full of struggles.
Seattle began the day 2½ games behind Oakland for the second AL wild card.
Information from The Associated Press was used in this report.