Chicago Cubs starter Jameson Taillon heads to the injured list while Kyle Hendricks nears a minor-league rehab stint

The first test of the Chicago Cubs starting pitching depth has arrived.

Jameson Taillon, who was scheduled to start Thursday at Wrigley Field, was placed on the 15-day injured list with a left groin strain.

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The move was retroactive to Monday, and the Cubs believe the right-hander will be ready to return soon after he is eligible. The Cubs called up Javier Assad from Triple-A Iowa to take Taillon’s place in the rotation, and Assad started Thursday against the Los Angeles Dodgers.

“Last year we didn’t have enough depth to withstand that,” team President Jed Hoyer said of Taillon’s injury. “Hopefully this year we have guys like Javy, and hopefully Kyle (Hendricks) comes back soon. It can never be an excuse. You have to have guys ready to fill those spots.”

Taillon signed a four-year, $68 million deal over the winter and is 0-2 with a 4.50 ERA in three starts. He threw five shutout innings Saturday against the Dodgers in Los Angeles.

Manager David Ross said Taillon felt some pain while playing catch on flat ground Sunday in Oakland, Calif. Assad began the season in the Cubs bullpen before being sent to Iowa, where he made one start, allowing two runs in 2 ⅔ innings on April 14.

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Hendricks, returning from right shoulder surgery, is scheduled to throw about three innings or 45 pitches in a bullpen outing Saturday at the Cubs spring complex in Mesa, Ariz. He likely would begin a minor-league rehab stint if he feels OK afterward.

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Hendricks would need at least two rehab starts to get to 75 pitches and be ready to return to the Cubs. The Cubs gave no timetable, but if he proceeds with no problems, Hendricks could be back by the second week of May.

“Right now it’s not a matter of health,” Hoyer said. “It’s a matter of building up his stamina.”

Hendricks’ four-seam fastball has hit 90 mph during some bullpen sessions, a few ticks above his typical velocity the last two years. Hoyer said that was by design.

“Actually we slowed him down in a way to work on his velocity,” he said. “There was a series of conversations in the spring. His velo had been kind of creeping down the last couple years, and we want to push his velocity up as much as possible.

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“When he was winning ERA titles he was touching 90. … He’s not (Oakland A’s rookie) Mason Miller throwing 102 mph, but when he throws 88-90, his changeup is that much more effective.”

The Cubs rotation entered Thursday with a 2.96 ERA, ranking third in the majors.