CHICAGO -- The White Sox placed left-handed reliever Garrett Crochet on the 10-day injured list prior to Thursday’s seven-inning doubleheader against Detroit with an upper back strain. The move was made retroactive to Monday.

Manager Tony La Russa believes that the issue could have something to do with the 21-year-old’s search for a smoother delivery, which dates back to Spring Training. He also knocked on wood when adding that Crochet should be ready to return at the end of this particular IL stint.

“There were times during Spring Training where he didn't feel like his delivery was all together, that he'd get a little cranky,” La Russa said. “But I think it's something that maybe progressed with time.

“More than anything else, it's strictly a precaution to back off now. A lot of it is just from getting his delivery together where it's nice and smooth.”

Crochet has an 0-2 record with one earned run allowed over nine innings in eight relief appearances during the 2021 campaign. The southpaw made five appearances covering six scoreless innings last season after being selected 11th overall in the '20 MLB Draft, but he had never thrown more than 26 pitches in a single outing before tossing a career-high 46 over three scoreless innings behind Michael Kopech in Sunday’s 8-4 victory.

During that 2020 stint, Crochet averaged 100.1 mph on his fastball and had the second-highest total of pitches at 100 mph or above in the Majors. He exited early from Game 3 of the ’20 American League Wild Card Series in Oakland due to a left flexor strain, a problem that he recovered quickly from with the help of an offseason throwing program. He has an average fastball velocity of 96.3 mph in ’21.

Crochet mentioned during a pregame Zoom on Wednesday that he’s focused on being more of a pitcher than a thrower in this full rookie campaign.

“If 100 comes back, it comes back,” Crochet said. “I’m just trying to make it through 162 games with this being my first full season. [I'm] getting in the weight room, feeling stronger every day, and as long as the arm’s feeling good, then I’m OK with whatever the velo board says.”

“The key is: do you command what you throw?” La Russa said. “He can rear back and fire but … if he throws 95 to 97 [mph] and gets rewards from that, and adds the breaking ball and occasional changeup, he's a star.”

Robert returns from the injured list

Outfielder Luis Robert was reinstated from the injured list Thursday, taking the place of Crochet on the active roster. Robert, 23, was placed on the injured list prior to Tuesday’s series opener as a precautionary measure when he developed flu-like symptoms, but all tests came back negative for COVID-19. He dealt with a positive case of COVID-19 during the offseason.

“I feel much better. I don't have any headache or fever or anything,” said Robert through interpreter Billy Russo, mentioning that a headache, fever and body aches arose Monday night, the team's off-day. “The only thing is I think my body is a little lethargic.

“But I think that's because the last few days, I have been in bed most of the time. I'm going to be good today.”

Robert is slashing .305/.356/.463 with eight doubles, one triple, one home run, six RBIs and 10 runs scored over 21 games this season, but he hasn’t really felt truly hot yet because of the cool April weather.

“It's a little uncomfortable to play with this weather, with cold weather,” Robert said. “That's one of the reasons why I'm trying to be more cautious with my swings and with my approach.

“I haven't really swung the bat really hard. I'm just trying to make good contact, but so far that has been good. The results have been good and I think once the weather starts warming up a little bit, my offense is going to start to warm up too. I have felt comfortable with my approach at home plate."

Third to first

• Infielder Danny Mendick was recalled from the team’s alternate training site in Schaumburg, Ill., as the 27th man for Thursday’s seven-inning doubleheader.

• The White Sox are 18-1 vs. left-handed starting pitchers since the start of the 2020 season. They are 4-1 in '21 entering Matthew Boyd’s Game 2 start Thursday.

They said it

“He's an energizer bunny when he's out there, so you've got to back him off some.” -- La Russa, on second baseman Nick Madrigal sitting for Game 1 on Thursday, but starting Game 2 and being ready for the weekend series vs. Cleveland.