Bad news Giants fans ... star safety Xavier McKinney will be out several weeks after he was injured in an ATV accident in Cabo during the bye week.
The 23-year-old broke the news on Monday morning, saying he flew out to Mexico for the Giants' off days ... but, unfortunately, got hurt while he was on a sightseeing ATV tour.
"I had an accident and injured my hand," he said in a note on Twitter. "The injury will keep me sidelined for a few weeks."
It's a big blow for New York, as McKinney -- who was named a team captain this season -- is a key player on the Big Blue's defense.