Paez, who spent the first-half of the season on-loan with Strasbourg, has suffered a "serious" shoulder injury.
Advertisement
Advertisement
Having made two appearances for River, the Ecuador international came on at half-time as they lost to Velez Sarsfield on Sunday, but lasted just 25 minutes before coming off.
Paez was seen clutching his arm after an aerial challenge and immediately signalled to the bench for treatment.
At fulltime, the Ecuadorian was seen sporting bulky strapping right across his left-side and shoulder. River are expected to deliver an update later today.