O'Reilly said that on Christmas Eve, he wasn't feeling well and at about 10:30 that night, he called the doctor.
"'Hey, I want to make sure this isn't appendicitis or anything like that,'" O'Reilly recalled saying. "Unfortunately it was, but it was good because we caught it in time and I didn't travel with it or anything."
After having the surgery on Dec. 25, O'Reilly said he was out of commission for about five days and on a liquid diet. He says he's fortunate it occurred during the three-day mandatory break because that cut down on the number of games he could've potentially missed.
Now after a practice under his belt that included some work on the power play, he thinks he'll be ready for Thursday night's match against the Chicago Blackhawks, which can be seen at 8:30 p.m. ET on NBCSN.
"I want to play tomorrow. I feel like I can for sure," O'Reilly said. "I might be a little rusty, but I feel like I'm ready to get back. I still think I can be effective and it's just a matter of talking with all the management and staff to make sure everyone's safe with it and I'll be safe with it."
If O'Reilly plays, Bylsma said it's likely that Sam Reinhart would stay in the middle. That would make O'Reilly, Jack Eichel, Reinhart and Zemgus Girgensons the top four centermen.
Brian Duff has more on the depth at that position and how they've fared in O'Reilly's absence in today's Sabres In :90.