The 25-year-old was involved in a collision with goalkeeper Vincent Enyeama during the goalless draw, and was replaced by Alan Pulido at half-time.
And, after the match, Hernandez confirmed he was suffering pain in his right knee.
"It really hurts," he is quoted as saying by Univision. "The goalkeeper fell on top of me, I'll wait for the tests."
However, Mexico team doctor Jose Guadalupe Vazquez moved to cool concerns of a serious problem, telling ESPN: "It is a bruise, but we have to rule out any ligament strain.
"He only has pain and he doesn’t have a history of knee instability.
"The bruise is in the middle part of the knee. We will have to wait to see whether it is a strain."
Hernandez could now miss Manchester United's trip to West Brom in the Premier League on Saturday.
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