Saudi Arabia captain Sami Al-Jaber is struggling to shake off an ankle injury in time to face Cameroon on Thursday.
The veteran striker missed training on Monday but was expected to undergo a light work-out on Tuesday.
Al-Jaber was the only Saudi player to pose any threat in their opening 8-0 humiliation against Germany last Saturday.
And his absence against Cameroon would be a major blow for a side desperate to salvage some pride against the African champions.
Al-Jaber, who once had a spell in England with Wolverhampton Wanderers, would be badly missed in a game the Saudis must win to remain in the tournament.
They complete their Group E campaign against the Republic of Ireland in Yokohama on 11 June.