Onuachu was forced out of Sunday’s Belgian league clash between his club Genk and Royal Antwerp in the 70th minute.
The 22-year-old was replaced by Ike Ugbo.
The striker had opened scoring for Genk in the first half before the injury.
He has scored 12 goals in the league this season after he scored 35 goals in all competitions in the last campaign.
Onuachu has thus joined Watford midfielder Oghenekaro Etebo who will not feature at the AFCON just as officials hope Osimhen will be fully recovered to be part of the tournament in Cameroon.