The Giants defense also lost linebacker David Mayo to a torn meniscus in his left knee. He started 13 games for the team last season.
Both were believed to be noncontact injuries. McKinney missed the team's intrasquad scrimmage on Friday but practiced in recent days. Mayo had been dealing with a knee issue.
There is hope that McKinney can return and his rookie season is not totally lost, sources told ESPN. A late-November return -- after the Giants' Week 12 bye week -- seems possible if all goes well with his recovery.
McKinney, who will eventually land on injured reserve with a designation to return, was a second-round pick earlier this year out of Alabama. He underwent surgery Wednesday at Hospital for Special Surgery in Manhattan. Foot specialist Dr. Martin O'Malley performed the procedure.
Mayo, a six-year veteran who re-signed with the Giants this offseason, is expected to have surgery Thursday. His timetable will be determined by the results of the procedure.
McKinney was expected to play a significant role in an already thin Giants secondary. He had a chance to work his way into a starting spot, or at the very least be a regular in sub-packages and on special teams.
"Xavier is a guy for us who's making a tremendous amount of improvement," coach Joe Judge said. "Look, we're still looking forward to getting him back out there on the field. I'm not a doctor, I don't have that timetable. I'm going to let those guys handle that. My only concern at this point is that he continues to work as hard as he can to get back on the field, and that we continue to develop him as a coaching staff, mentally, that he makes progress within the situational awareness and overall understanding of our schemes and the league tendencies in his time off the field."
McKinney's absence puts even bigger emphasis on second-year safety Julian Love to provide stability alongside Jabrill Peppers. Love has impressed early in training camp after finishing last season strong.
The Giants' secondary will have a vastly different look than expected only a few months ago. Cornerback DeAndre Baker is on the commissioner's exempt list and faces armed robbery charges from an incident earlier this offseason. He's unlikely to ever play another snap for the Giants. Third-year cornerback Sam Beal also opted out of the season at the start of camp.
The Giants tried to sign a veteran replacement in Ross Cockrell, but that deal fell apart despite an agreement being in place. They hope to sign former Arizona Cardinals cornerback Brandon Williams in the coming days after he completes the COVID-19 testing and a physical, but they have now lost McKinney for at least a couple months.