PITTSBURGH -- Rockies left-handed pitcher Tyler Anderson will have surgery on his ailing left knee, and it won’t be known until after the operation whether he can return this season, manager Bud Black said Tuesday.

At any rate, the Rockies -- going with a four-man rotation until Saturday, when a fifth starter becomes necessary -- will have to find a long-term replacement. Righty Jeff Hoffman, who has made one Major League start this season but has done the rest of his duty at Triple-A Albuquerque, appears to be a logical candidate.

Anderson (0-3, 11.76 ERA in five starts) attempted to pitch through knee issues at the beginning of the season, but he was on the injured list for 17 days in April. Despite that stint, his performance never stabilized.

Anderson was optioned to Triple-A Albuquerque on May 4 after giving up six runs and seven hits in four innings during a loss to the D-backs at Coors Field, but he never pitched for the club. Instead, he has been consulting with doctors.

Black did not have a date for when Anderson would undergo the operation.

Anderson, 29, is 18-24 with a 4.69 ERA across four Major League seasons. He was the team’s top Draft pick (20th overall) out of the University of Oregon in 2011. He previously had arthroscopic surgery on his left knee during the '17 season, which he finished 6-6 with a 4.81 ERA, returning to the active roster before the end of the year.

This could finally be the opportunity for Hoffman, 26, to fulfill the expectations that came along with being a key prospect acquired in the trade that sent star shortstop Troy Tulowitzki to the Blue Jays in 2015. In four seasons, Hoffman has made 38 Major League appearances, including 24 starts.

Hoffman started against the Nationals on April 23 and gave up four runs in five innings of a 6-3 loss. All of the runs came in the third inning with no outs, but Hoffman retired nine of the final 10 batters he faced.

After returning to Albuquerque, Hoffman skated through his first three starts, going 3-0 with a 1.96 ERA, .143 batting average against and 27 strikeouts to five walks. However, the last start went awry -- eight runs on nine hits in 5 2/3 innings against El Paso on Friday.

De La Rosa ramping up

Left-handed pitcher Jorge De La Rosa, who signed a Minor League contract with the Rockies on April 5, is ramping up his workload in extended spring camp after having his progress slowed by an oblique injury that occurred about a week after he signed.

“Now he’s full-go off the mound, and at some point this week, he’ll get into games,” Rockies senior player development director Zach Wilson said. “This is his Spring Training, because he didn’t have one. He’s in shape. We’ll get him a few outings and just see what happens at that point.”

De La Rosa pitched for the Rockies from 2008-16, mainly as a starter, before joining the D-backs (2017-18) and Cubs (2018) as a reliever. He's hoping to contribute to Colorado's bullpen when deemed ready.