The Senegalese international became the Potters third signing of the winter on Wednesday evening after completing the formalities of his £14M move from Turkish side Galatasaray.
Lambert said: “He had one or two little things to tidy up today so he wasn't with the group.
“But he is in the building tomorrow and he will train with us for the first time, so we will have a close look at him then.
“He says he is ready to go, he wants to play matches and is clearly in good shape, but I will judge everything tomorrow."
He added: “He is certainly going to improve the side moving forward because he is a very talented boy, who is hugely important for his country and has been equally as important for Galatasaray this season."