McKinney was back with the team on Monday, according to a source. He detailed the injury in a Twitter post.
The ascending safety says he was injured on a guided sightseeing tour.
Later Monday the Giants placed McKinney on the reserve/non-football injury list, meaning he will miss at least four games.
The Giants return from their bye to host the Houston Texans on Sunday at MetLife Stadium. They will now be without their defensive playcaller and a captain for several weeks. McKinney will also at least miss games against the Detroit Lions, the Thanksgiving matchup at the Dallas Cowboys and a home game against the Washington Commanders.
Coach Brian Daboll gave his players just about the entire week off after a 27-13 loss last Sunday in Seattle. McKinney posted a story on Instagram from Cabo San Lucas early last week.
The Giants (6-2) didn't return to work until Monday. They have upcoming home games against Houston and the Detroit before a Thanksgiving matchup with the division-rival Cowboys.
McKinney, 23, was a second-round pick out of Alabama in the 2020 NFL draft. He became a full-time starter last year.
McKinney is currently fourth on the Giants with 37 tackles. He also has a sack, two tackles for loss and four passes defended.
This isn't the first time that a current or former NFL player has been involved in an ATV accident. Malik McDowell, a second-round pick by the Seahawks in 2017, had his career derailed by an accident before he ever played an NFL game, and former receiver Mohamed Massaquoi had his left hand amputated when his ATV rolled over in 2018.