CHICAGO -- On Thursday, the Cubs' John Lackey threw his second bullpen session since going on the disabled list, and he is expected to start on Sunday in the series finale against the Giants. However, reliever Pedro Strop had a setback in his rehab from a torn meniscus in his left knee, and will need the full six weeks to rehab.
The Cubs want to see how Lackey feels on Friday, and if all is well, he'll start Sunday. He's been sidelined since Aug. 15 with a right shoulder strain.
Strop, who has been on the disabled list since Aug. 11, tweaked his right groin on Wednesday and his rehab will be slowed down. When he was initially injured, the prognosis was that it would take the right-hander four to six weeks, and it now looks as if the six-week timeline is more accurate.
The Cubs did get good news regarding reliever Héctor Rondón, who has been out since Aug. 17 with a right triceps strain. Rondon will begin a rehab assignment with Triple-A Iowa and was scheduled to pitch Saturday and Monday.
• Chris Coghlan (right rib contusion) was activated from the disabled list along with right-handed pitcher Joe Smith (left hamstring strain), and the Cubs also selected the contract of right-hander Jake Buchanan from Iowa. Buchanan, 26, went 12-8 with a 4.34 ERA in 24 appearances (22 starts) with Iowa. He was with the Astros in Spring Training, and released on March 31, then signed a Minor League deal with the Cubs and joined Iowa on April 18.
In 22 appearances in the big leagues, Buchanan has a 4.06 ERA, giving up 20 earned runs over 44 1/3 innings.
Smith and Buchanan give the Cubs two fresh arms, but Aroldis Chapman pitched in his third straight game on Wednesday, and manager Joe Maddon said he was not going to use the lefty on Thursday, and possibly Friday.
So, who's the Cubs closer?
"I don't know," Maddon said. "I still have to take a show of hands to find out who's available."
• Addison Russell entered Thursday leading all National League shortstops with 86 RBIs this season, and has made several acrobatic plays. Maddon says he's more impressed with Russell's offensive development.
"The stuff you're seeing on defense, he's just a great athlete," Maddon said. "All the gymnastics stuff he's able to do, he's a great dancer, he's got good feet, the play he made [Wednesday] night, I think that's always been there. I think the offensive side has really grown the last two years."
• Chapman took time on Thursday to visit with patients at Lurie Children's Hospital in Chicago. He brought teddy bears and Cubs caps to distribute to the kids and posed for photos.

• In his past 12 games, reliever Justin Grimm has given up one earned run over 11 innings while striking out 17. The right-hander may have gotten a wake-up call when he was optioned to the Minor Leagues in late July.
"There was probably that moment when you sit there and you talk to yourself, and it might have helped," Maddon said. "The curveball has been fantastic [since he came back], and that's his pitch, that's his bread and butter. There's more strike throwing. There's a more relaxed demeanor. If he misses a couple times, he doesn't continue to miss."
• This is catcher David Ross' last season, and he asked teammate Matt Szczur for an autographed Villanova football jersey for his "man room" at home. Szczur, who played football for the Wildcats, had no problem getting one and autographed it for Ross.
"It's cool that he wanted it," Szczur said.

Anthony Rizzo also presented Ross, 39, with some fishing poles to use once his playing days are over.