Team doctors diagnosed Paulino with a torn ulnar collateral ligament in his right elbow, the club announced on Friday. That usually leads to elbow reconstructive surgery, commonly known as Tommy John.
Paulino will get a second opinion from Dr. Lewis Yocum, a specialist in the field, but Paulino expects to have surgery.
"There's going to be surgery. It's going to happen. They gave me two options -- rest or surgery -- and I prefer to have surgery," Paulino said.
Earlier this year, the Royals lost closer Joakim Soria, starter Danny Duffy and reliever Blake Wood to Tommy John surgery. Typical recovery time is 10 to 14 months.
"It really surprised me. I was just doing my rehab so I would be able to start next Monday, and it just happened," Paulino said.
Paulino, 28, had emerged as one of Kansas City's best starters this season after recovering from forearm tightness which put him on the disabled list at the end of Spring Training. Since June 6, he has been sidelined with a right groin strain, leaving the first inning of a game against the Twins. That ailment is completely healed.
In seven starts this season, Paulino had a 3-1 record and 1.67 ERA with 39 strikeouts in 37 2/3 innings.
"I think I've shown everybody what I can do if I'm healthy," he said.
Paulino felt his elbow pop late in a rehabilitation assignment start on Wednesday night for Double-A Northwest Arkansas. The right-hander gave up three runs, four hits and two walks in three innings. He made 54 pitches.
"I finished the game; I was supposed to throw three or four innings and my last 12 or 15 pitches were really painful," Paulino said.
Paulino doesn't believe the torn ligament was related to the forearm flexor ailment he had during Spring Training, but manager Ned Yost feels it's a danger faced by many pitchers.
"We knew he was pitching, like all pitchers do, with some potential for this to happen," Yost said. "But he'd been throwing the ball really well and this wasn't even in the equation. This was nothing that he's felt all year long."
The loss of Paulino means that right-handers Vin Mazzaro and Luis Mendoza will get additional opportunities to stay in the rotation with Bruce Chen, Luke Hochevar and Jonathan Sanchez. But the Royals also will keep an eye on potential starters in their Minor League system.
To have four pitchers with Tommy John surgery in one year is daunting, but Yost has noticed many pitchers around baseball facing it.
"I don't know why there's such a big number of guys going down with Tommy John surgeries this year, but we're not immune to it by any stretch of the imagination. Our numbers have added greatly to it," Yost said. "I don't think I've ever been around a team where two guys have had to have Tommy John, let alone four. You just deal with it and move on."
That's what Paulino plans to do.
"Many pitchers have done it before and it happened to me now. I'll just try to be strong and I have the support of my teammates, the manager and my wife," he said. "I'm looking forward. I know it's going to be a long recovery, but I believe I will be back."
Dick Kaegel is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.