When Shota Imanaga returned to the rotation from a hamstring strain, the Cubs looked to have a solid group that would at least tide them over until the trade deadline: Matthew Boyd, Shota Imanaga, Cade Horton, Colin Rea and Jameson Taillon.

Then, Taillon’s calf injury put a hitch in those plans.

[Jameson Taillon injury: Cubs pitcher vows ‘best case’ diagnosis in update]

Taillon, who was scheduled to make his 18th start of the season when the Cubs hosted the St. Louis Cardinals on Saturday, suddenly bowed out Friday when the team announced that he would be missing significant time with a strain he sustained in a workout. The Cubs recalled lefty Jordan Wicks in a corresponding move.

In Taillon’s place, the Cubs plugged the gap temporarily with a bullpen game opened by Drew Pomeranz.

When Pomeranz loaded the bases with just one out in the first inning, Chris Flexen jumped in to minimize the damage.

“It was another really good outing,” Cubs manager Craig Counsell told reporters of Flexen after the game. “I thought he gave us what we needed. He’s continuing to be a really valuable member of our bullpen.”

[Cubs takeaways: What we learned in bullpen-game home loss to Cardinals]

The Cubs sent seven of their nine relievers to the mound on Saturday, hoping to secure the series. However, an uncharacteristic five-run eighth inning and a blown save from Brad Keller resulted in Chicago falling 8-6 to their bitter rivals.

“I’ve just got to make better pitches in those moments,” Keller told reporters of the Cardinals’ pinch-hit, three-run home run that put the nail in the Cubs’ coffin. “It’s frustrating, but we’ll live to fight tomorrow.”

Saturday aside, Keller and the rest of the Cubs’ bullpen have been great this year. Their 2.36 ERA since May 1 is the best mark in MLB, while their 3.30 ERA over the whole season is third in the league.

But the afternoon was a stark reminder that the Cubs won’t be able to ride on their relievers’ coattails every fifth day while Taillon is out.

Additionally, the July 31 trade deadline is still weeks away. While Cubs president of baseball operations Jed Hoyer has spoken of his broader plans to ‘get creative’ with his moves and improve the rotation, it’s highly unlikely any of the big names linked to the Cubs — such as the Pittsburgh Pirates’ Mitch Keller or the Miami Marlins’ Sandy Alcantara — will be on the Cubs’ roster when Taillon’s next start is scheduled.

The fifth spot in the Cubs’ rotation isn’t slated until July 11 against the Yankees in New York City, so Counsell and his staff have plenty of time to figure things out. However, there’s still a lot of mystery on the current roster to unpack.

For one, Counsell made it clear that Wicks is not slated to make any starts when he spoke in a press conference Friday.

“He’s there to pitch in the bullpen — we’ll go from there,” Counsell told reporters.

Wicks also did not feature out of the bullpen on either Friday or Saturday. He made 17 starts for the Cubs across 2023 and 2024, but he has a 5.05 ERA in those outings.

There’s Ben Brown, who began the year in the Cubs’ rotation and posted a 6.13 ERA in 14 big-league starts. He was sent down to Triple-A Iowa to accommodate Imanaga’s return to the active roster, and it’s highly unlikely the Cubs will bring Brown back this soon as he is set to make only his first appearance for the I-Cubs on Sunday.

The member of the Cubs’ bullpen who is the most stretched out at this point is Flexen.

This year, he has already pitched the fourth-most innings among Cubs relievers (32.2), despite not making his debut until May 2. Even then, Flexen displayed more endurance than a typical high-leverage reliever, throwing 54 pitches across three scoreless innings.

Flexen has more recently worked season-highs in both innings and pitch count — he threw four scoreless frames in Houston on June 27, and his 64 pitches across 3.2 innings of relief Saturday were the most he’s thrown this year.

Flexen also has plenty of starting experience. He made 30 starts for the White Sox last season, pitching to a 4.95 ERA over 160 innings. And while those numbers don’t exactly jump off the paper, the 31-year-old’s 0.83 ERA this season should be proof enough that the change of scenery has turned him into one of the league’s top pitchers.