Coach Kyle Shanahan said Robinson is believed to have suffered a high-ankle sprain in Sunday's win over the Dolphins, Vic Tafur of The Athletic reports.
Robinson was injured in the second quarter and had to be carted to the locker room. He was already replacing De'Zhaun Stribling as the Niners' WR3 after Stribling suffered a serious ankle injury in Week 1 against the Rams that is expected to sideline the rookie receiver for 10 weeks. San Francisco will have to delve deeper into its wideout depth chart, with Jacob Cowing, Jordan Watkins and KhaDarel Hodge the only healthy bodies behind Mike Evans (hip) and Deebo Samuel.