Hernandez went down and appeared to be stretching out his hamstring. He was replaced by Raul Jimenez in the 47th minute of the contest.
At the time, the game was level 1-1 thanks in part to a first-half penalty the West Ham man had drawn on Belgium defender Laurent Ciman, which Andres Guardado converted. The game finished a 3-3 as Mexico got a brace from Hirving Lozano to cancel out strikes from Eden Hazard and of Belgium's own from Romelu Lukaku.
Mexico faces Poland in another international friendly on Monday, but it remains to be seen if manager Juan Carlos Osorio would risk Hernandez if there is any possible lingering injury.
Hernandez wasn't the only player Mexico had forced off during the match, with Edson Alvarez substituted shortly after coming on.
"They're being observed and we don't know the seriousness of the injuries," Osorio said after the match.
If Hernandez does miss Mexico's Monday friendly, his next contest would be West Ham's Premier League match against Watford on Nov. 19.
The striker has scored four Premier League goals this season for the struggling Hammers since his summer move from Bayer Leverkusen.