The centre-back turns 32 next week and has 10 senior caps for Italy, recently featuring in the Nations League.
He went off during the 1-0 victory over Fiorentina at the weekend and tests have shown there is a Grade I lesion to the femoral bicep in his right thigh.
A statement from the club warns his condition will be monitored on a daily basis, but the medical staff are not sure when they will be able to have Toloi back at their disposal.
Considering the nature of the injury, it is likely to be at least two to three weeks.
Another defender, Jose Luis Palomino, is suspended after failing a pre-season doping test.