If Nadal had a torn ACL he'd be on crutches. We can safely say 100% it isn't his ACL. Probably just a bad case of the same tendinitis he's always had.
Depends. Mickey mantle played years on a torn ACL and Hines Ward for the steelers played his entire career without an ACL After he tore it(in high school)- he was able to stregthen all his muscles and tendons around them.