SAN DIEGO -- Justin Steele headed out to left field at Petco Park on Saturday afternoon and went through a routine round of catch, with a member of the Cubs’ training staff observing. By all accounts, no alarms were sounded in the left-hander’s first test since he exited his last start due to injury.

Even with that positive step forward, the Cubs elected to place Steele on the 15-day injured list (retroactive to Thursday) with a left forearm strain prior to a 6-0 loss to the Padres. Cubs manager David Ross called it a precautionary move, but it was nonetheless another challenge for a club trying to stop its season from spiraling.

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“It's never easy, right?” Cubs pitching coach Tommy Hottovy said. “It's never like, ‘Oh, everybody's locked in and rolling all together.’ No, I think that's why you do all the work you can to build as much depth and pieces as possible that you feel like you can go out and compete with.”

Hottovy said the primary function of Saturday’s throwing session for Steele was to get “a bearing of where he was” health-wise. A trip to the IL was likely the outcome no matter how that workout went, given how important Steele is for the stability of the rotation.

The way the Cubs viewed the situation, it did not make sense to risk sending Steele back to the mound in San Francisco at the tail end of this three-city road trip against the Padres, Angels and Giants. This way, Steele will miss two starts at a minimum, giving him ample time to rest, recover and make sure the setback is no more serious than expected.

Through 12 starts this season, Steele is 6-2 with a 2.65 ERA, 58 strikeouts and 16 walks in 68 innings.

“[We’re] making sure we're just taking every precaution,” Ross said. “It just made a lot of sense.”

Right-hander Hayden Wesneski -- part of the Opening Day rotation -- will move out of the bullpen and assume Steele’s spot. Right now, Wesneski projects to start on Tuesday against the Angels and again on June 11 against the Giants.

Steele would be eligible to be activated for the Cubs’ home series against Baltimore from June 16-18. Hottovy noted that the pitcher would likely have two bullpen sessions prior to taking his next turn.

To fill Steele’s roster spot, the Cubs recalled catcher Miguel Amaya from Triple-A Iowa.

Steele, 27, left his outing against the Rays on Wednesday after experiencing what he described as “throbbing” in his forearm between pitches. The lefty logged three perfect innings, but Ross pulled the plug after 29 pitches. An MRI exam on Thursday showed a “mild” strain, according to the ballclub.

“We still felt like it was a good decision to get me out of the game before we went out there and made things worse,” Steele said on Friday. “But, it was obviously really good news to hear that it was just a mild strain in the muscle. That's what we wanted to hear.”

Ross echoed that sentiment.

“This was great news,” said Ross, given the nature of the injury. “I think it's much better news than we [initially] thought and he feels great about it. And being able to work his way back and not miss a lot of time just feels like it's going to play out really well for the full season.”

To date, the trio of Marcus Stroman (2.59 ERA), Drew Smyly (3.56 ERA) and Steele have helped the 25-32 Cubs avoid falling too far out of a wide-open National League Central race. Smyly allowed three runs over 5 2/3 innings on Saturday, but former Cubs pitcher Yu Darvish handcuffed Chicago’s lineup over seven dominant frames.

“Darvish is is a heck of a pitcher,” Smyly said. “He's been doing it for a long time. Cubs fans know. And he was on tonight. He had a really good game. Anytime you're going up against a pitcher like that, you know you've got to be pretty sharp.”

Jameson Taillon (7.05 ERA) appeared to take a step forward in his outing on Friday. Veteran Kyle Hendricks is also back in the fold after missing most of the first two months while coming back from a shoulder issue. Wesneski and Javier Assad are the top depth options while Steele is out, but they have experienced the expected ups and downs of younger arms.

The challenge for the Cubs has been to get everything functioning properly at the same time.

“There’s always something to do,” Hottovy said. “That’s why it's important to have pieces that you feel like can fill in those gaps when you need to.”