When the pain continued to linger, team medical director Dr. Tim Kremchek and head trainer Mark Mann recommended an MRI exam Wednesday.
"Our worst fears were realized," Krivsky said. "His pain went more from the forearm to closer to the elbow. [The MRI] was a very smart thing for us to do so we could find out what it is. Unfortunately for everybody, it's a serious injury."
Denorfia will go on the disabled list and will be out for at least six months. Kremchek is expected to perform the operation Tuesday in Cincinnati.
"We know what kind of worker Deno is and that he'll get back to where he was," Krivsky said.
Last season, Denorfia batted .283 in 49 games over four callups with the Reds. He batted .349 in 83 games with Triple-A Louisville.
Denorfia was batting .264 (14-for-53) in 20 games this spring and was a finalist for the final bench spot on Cincinnati's 25-man roster. His injury leaves outfielder Norris Hopper and catcher Chad Moeller left in the running to be the 25th man.
"That's unfortunate for him," Hopper said. "A couple of days left to break camp and he comes down with this kind of injury. I just hate it for him. He's got the whole season to sit around and try to get back from it."
Hopper has not played since March 19 because of a bruised right heel. It wasn't known when he could return to action.
"To tell you the truth, I can't really say. I don't know," Hopper said. "It's pretty close. I'm just trying to get the soreness out. It's crazy. Being my first big league Spring Training and having an opportunity to compete for a job, and maybe win one, to come down with this injury, yeah, it's real tough."
Meanwhile, Moeller entered Thursday batting .321 (9-for-28) with one homer and seven RBIs in 21 games. If the 32-year-old veteran makes the club, it would be as a third catcher behind David Ross and Javier Valentin.
A flurry of roster moves accompanied the news of Denorfia's injury. Fifth-starter candidate Bobby Livingston and reliever Gary Majewski were optioned to Louisville. It was an expected move for Majewski, who is catching up after being out most of camp with a sore shoulder.
Infielders Jerry Gil (sore right elbow) and Jeff Keppinger (broken finger), starting pitcher Elizardo Ramirez (sore right shoulder) and lefty reliever Bill Bray (bruised fingertip) will be placed on the disabled list and remain in Sarasota for extended Spring Training.
Lefty closer Eddie Guardado, who is still rehabilitating from Tommy John surgery, will go on the 60-day disabled list. Guardado will go north with the club.
That means the fifth-starter battle is down to Kirk Saarloos and Matt Belisle. If he doesn't win that job, Saarloos would be get one of the two remaining bullpen spots. The final bullpen spot is down to Victor Santos, Jared Burton and lefty Jon Coutlangus.
Burton could have the inside track for the role since he's a Rule 5 player. The right-hander would have to be offered back to Oakland if he's not on the 25-man roster all season.
Cincinnati, which has 28 active players left in Spring Training, will likely finalize its roster Friday. The club will break camp after Friday afternoon's game vs. the Devil Rays.