Reds manager Jurgen Klopp revealed that the 26-year-old, who was recently cleared of doping charges by UEFA, will only be able to join first-team training after three to four weeks.
Klopp said: "Mama is injured. He had a little issue with his Achilles when he was playing - one day on, one off, this kind of thing.
"When he had his little 'break' he used the time to have a little bit of treatment and that now means another three or four weeks before he can train again.
"There was no surgery, he is just not about to train at the moment. He has got some rehab of course and it's not too good a situation for him, us, everybody.
"He's not available at the moment but he is doing rehab. We will see how he reacts to that and then when he can play again."