LAS VEGAS — As the Rockies opened a six-game road trip through Las Vegas and Chicago, the rotation took a hit, not just for this series but for the foreseeable future.

Rockies manager Warren Schaeffer confirmed on Friday afternoon at Las Vegas Ballpark that “it’s looking like surgery” for Chase Dollander on his right ulnar collateral ligament (UCL). The date for any surgery has yet to be determined as there is still a pre-op appointment “coming up soon,” per Schaeffer.

Undergoing UCL surgery would sideline the 24-year-old former first-round pick through at least the end of this season.

Dollander last pitched on May 14, lasting just one inning in Pittsburgh before being taken out of the game. He was placed on the 15-day injured list the next day with a right elbow strain.

On Friday, before the Rockies opened a three-game set against the A’s in Las Vegas, Dollander was moved to the 60-day injured list. With that move, Colorado called up left-hander Sean Sullivan, ranked as the 11^th-best prospect for the Rockies, for his first MLB start.

“The rehab process just wasn’t getting any better, so second opinions and that sort of thing,” Schaeffer said of what eventually caused Dollander to head toward surgery.

Dollander told The Denver Gazette and other reporters on May 29 that he was hoping to avoid what he called “the worst-case scenario” with surgery.

“I don’t think there’s any point for that unless the worst-case scenario happens,” Dollander said, referring to MRIs or other tests that might reveal more of the severity of his injury. “I’m praying to God that doesn’t happen. I’m taking it day by day and making sure we’re doing everything we can.”

In 10 games (including three starts) covering 44 innings, Dollander posted a 3.89 ERA while striking out 47 and walking 18. Opponents hit .238 against him.

All of those numbers were marked improvements over his rookie season in 2025 when Dollander went 2-12 with a 6.52 ERA in 98 innings over 21 games.

The 23-year-old Sullivan was 5-3 with a 5.60 ERA in 11 starts covering 54 2/3 innings in his first season with Triple-A Albuquerque before the call-up. He was selected in the second round of the 2023 MLB draft by the Rockies, who used the 46^th overall pick to snag the Wake Forest pitcher.