Volker Finke's men had their first training session since landing in Brazil on Tuesday, but midfielders N'Guemo and Salli were limited to muscle toning and stretching exercises.
It leaves little time for the two to be fully fit ahead of Cameroon's FIFA World Cup opener, but Finke is hopeful both players will return to a full schedule by the end of the week.
"Within two or three days, everything should return to normal for Salli and N'Guemo," Finke said at a press conference.
Finke also confirmed that Jean Makoun will not start Friday's game, despite returning to training following an ankle injury.
The Lens midfielder joined in Cameroon's latest session, and should be among the substitutes against Mexico.
"I feel better and better, and I should even say that I am feeling very well," Makoun commented.
As well as Mexico, Cameroon will also face Croatia and Brazil in Group A.
