CINCINNATI -- The injury to D-backs right-hander Humberto Castellanos has opened a spot in Arizona’s rotation, and manager Torey Lovullo is anxious to see who will step up and grab hold of the opportunity.

Castellanos suffered a forearm strain during his May 31 start against the Braves. While not giving a specific timeline for Castellanos' return, Lovullo said it would be measured in weeks.

So the search is on for a rotation replacement.

"Fluid," Lovullo said of the situation. "We’ve got to throw all the names in the ring right now when we’re backed up like this. We’ve got a lot of really good internal candidates, and we want somebody to step up. I think that’s the spirit of this game. We’ve got to find a way to get it done and continue earning things. I think that’s the overall mindset as a team and an organization coming off of what we did last year. 

“I want everybody to earn everything, including that fifth spot."

Tyler Gilbert got a shot Tuesday night, but things didn't go as he hoped. The Reds jumped him for seven runs (six earned) on five hits and two walks over 1 2/3 innings as they beat the D-backs, 14-8, at Great American Ball Park.

Lovullo did not want to say after the game whether Gilbert would get another start, preferring to talk things over with his staff first. Given the results Tuesday, along with the fact that the team has other rotation candidates, it seems likely someone else will be on the mound when Castellanos' spot comes up Sunday in Philadelphia.

One candidate could be Luke Weaver. The right-hander, who has been on the injured list since the first week of the season with right elbow inflammation, allowed just one run on three hits over four innings in his second rehab appearance for Triple-A Reno on Tuesday.

If Weaver stays in a regular five-day rotation, that would line him up to pitch again Sunday, which is when Arizona will next need a starting pitcher.

Another name to keep an eye on, though likely not for this Sunday, is Dallas Keuchel.

The D-backs signed the veteran left-hander to a Minor League deal Monday. He had been released by the White Sox on May 30 after going 2-5 with a 7.88 ERA in eight starts.

Keuchel has a history with Arizona pitching coach Brent Strom dating back to their days together with the Astros. In fact, Keuchel won the American League Cy Young Award under Strom's tutelage in 2015.

Keuchel reported to the D-backs Spring Training Complex at Salt River Fields, where he has thrown a bullpen session.

"We obviously need to have him throw some bullpens and get built back up a little bit," D-backs general manager Mike Hazen said Monday. "And then we’ll see. Obviously there’s some adjustments that Strommy needs to make with him and our staff. Hopefully we can get him back on track. But we’ll see."

After Tuesday’s game, Lovullo announced that Keuchel would be reporting to Cincinnati on Wednesday to join the team's taxi squad to provide coverage in case of a COVID-19 outbreak. It would also give Keuchel a chance to work with Strom.

Rookie Corbin Martin, currently with Reno, is another fifth-starter possibility that bears watching.

"We're figuring that out," Lovullo said after Tuesday's game. "We're having conversations about it, and they'll continue through the rest of the night and probably into tomorrow. We'll figure it out. We're gonna find a way to get that fifth spot shored up."