Hernandez was forced off at half-time in Mexico's draw with Nigeria after colliding with goalkeeper Vincent Enyeama.
Now the United striker is due to undergo tests, although he admitted after the game to having some concerns about the problem.
Hernandez told Univision: "I don't feel good, the [Nigerian] goalkeeper fell on top of me, I'll wait for the tests."
Mexico national team doctor Jose Vázquez told ESPN Deportes that there was no ligament damage.
"We have to wait to see how it evolves and to run the relevant tests," he said.
"It's a blow, but we rule out the possibility of a knee ligament strain. There is only pain and there is no indication of instability in the knee."