Pedro Strop suffered a setback in his recovery from a knee injury, but the hiccup currently falls in the "minor" category.
Strop strained his groin while working out Wednesday and will shut down for a week or so. Once he gets the green light, he will head out on a rehab assignment and the Cubs still plan on having the veteran setup man available in late September and for a potential World Series run.
Meanwhile, the Cubs received good news Thursday as John Lackey's bullpen session went well and he is on track to return from the disabled list and start Sunday's series finale against the San Francisco Giants.
Lackey has been dealing with a sore shoulder. He spoke to the media before Thursday night's game and said he feels good to go.
When he does return, Joe Maddon acknowledged the Cubs could still go with a "soft" six-man rotation to help keep starters fresh down the stretch. That means Mike Montgomery will likely still get a few starts in the final month of the season, but could appear out of the bullpen in between turns in the rotation.
[RELATED - 5 things we learned about the Cubs in August]
Hector Rondon (triceps) is heading out on a rehab stint with Triple-A Iowa, where he will throw Saturday and then likely Monday. He could rejoin the big-league club sometime next week.
MLB
The Cubs also got some reinforcements with rosters expanding Thursday, activating veterans Joe Smith and Chris Coghlan off the disabled list and calling up right-hander Jake Buchanan from Triple-A.
Maddon immediately inserted Coghlan into Thursday's lineup and said the two pitchers are available, which should help a bullpen that has been taxed of late.
Maddon said closer Aroldis Chapman was unavailable Thursday and possibly Friday after working all three games of the Pirates series.
As of his media session a couple hours before Thursday's game, Maddon still didn't know who else would be unavailable out of the bullpen besides Chapman.
"When you're winning often, you're gonna use up a lot of good bullpen," Maddon said. "That's what happens. When you're winning a lot of games, the guys that you normally like to have in the game are going to get utilized a lot in a lot of close games and thus they get tired.
"It's just part of the way this thing flows."
[MORE - How Kyle Hendricks transformed into a Cy Young-level performer]
With Thursday's moves, the Cubs' big-league roster sits at 28 players.
In addition to the injured players returning to full health, more call-ups are still on the way, likely including reliever Spencer Patton (who has shuttled back and forth between Iowa and Chicago this season), young outfielder Albert Almora (who spent time with the big-league club earlier in the summer when Jorge Soler was on the DL) and entertaining infielder Munenori Kawasaki.