Seth Rollins is currently being rested due to a bad back and isn’t expected to wrestle for at least the next couple of weeks.
According to the Wrestling Observer Newsletter, he’s been dealing with the injury for a while and even before the Royal Rumble, knew that he would need to take some time off to heal.
He apparently could wrestle right now if he needed to, but WWE felt that it’s a better idea to rest him up and try to get him as close to 100% as possible since he’s going to be in the main event at WrestleMania.