Sylvester Stallone isn't just a huge fight fan, he's also a minority owner of the UFC -- and tells TMZ Sports he's genuinely concerned for Conor McGregor after his latest arrest.
"This is a crossroad in his life," Stallone told us in Beverly Hills ... referring to both the arrest AND the fact he's coming off a huge loss to Khabib Nurmagomedov.
"If he can't overcome his fear and beat this man, I think it'll plague him for the rest of his life.