Diao, along with international colleague Diouf, failed to impress during the 1-1 draw and must now hope to find form not seen by a wary Anfield faithful when he is fit if he is to remain at the club beyond the summer.
Gerard Houllier said: "Salif injured his calf playing for the reserves and with a calf injury it takes time to recover from. He will be out for at least three weeks."