Drew McIntyre had been dealing with a bad neck for several months but was working through it until the Day 1 event where he was written off in an angle backstage after being attacked by Madcap Moss and Baron Corbin.
The belief was that due to him dealing with cervical neck strain with severe contusions, he would return before WrestleMania, but miss the Royal Rumble.
That didn’t happen as McIntyre made a surprise return in the Men’s Royal Rumble match. It was reported while he was on the sidelines that he was taking the John Cena approach to rehab.
McIntyre made an appearance on Sports Guys Talk Wrestling where he explained how he came back so quickly.
"They dropped a lighting rig on my head and I came back three and a half weeks later. I think everybody, including the doctor, was surprised at how soon I was able to comeback. They told me, 'You're not making the Rumble. WrestleMania is possible, but let's say it's unlikely right now.' 'Okay Doc, no problem. I went straight to rehab and I've always had the John Cena approach to rehab with every injury.”
He asked what the most he can do to get the best benefit and was doing rehab twice a day for six days a week so he did just that. He took Sundays off to relax. Thus, when he saw the doctor a few weeks later, the doctor said he was a cyborg and was cleared.
H/T to Fightful for the transcription