PHILADELPHIA — Just when it looked like the Cubs’ bullpen might be days away from returning to full strength, the lineup took another hit when outfielder Jason Heyward was scratched from the lineup Wednesday with an injured left knee.

The Cubs are calling it inflammation, and Heyward insisted it won’t put him on the 10-day injured list. But he also said the issue began when his knee ‘‘kind of locked up’’ as he went to get out of bed in the middle of the night, causing a ‘‘sharp pain’’ as he tried to bend it. That potentially sounds like more than a one- or two-day issue.

‘‘Not as of right now,’’ manager Joe Maddon said. ‘‘Right after he hit [in the batting cage], he reported that it was still there but not awful. We’ll play it day by day, but what I’m hearing is it’s nothing that we should be concerned about right now.’’

Heyward said the knee loosened as he got active during the day and took swings in the batting cage.

‘‘It’s a lot better than I thought it would be,’’ he said.

Maddon said Heyward might sit out Thursday, too, with the Phillies scheduled to start left-hander Drew Smyly.

The left-handed-hitting Heyward, who is having his best season with the Cubs, has been the leadoff man the last two weeks. Second baseman Tony Kemp took his place at the top of the order Wednesday against Phillies ace Aaron Nola.

‘‘Rest will help it,’’ Heyward said. ‘‘It’s not going to be an IL thing. Sometimes you need to stop to not make something worse.’’

Hearts with Jake

Phillies right-hander Jake Arrieta, the 2016 National League Cy Young Award winner and World Series hero for the Cubs, finally was shut down after pitching through the increasing pain of a bone spur that has bothered him for much of the season. He is scheduled for an MRI exam Thursday and said he anticipates needing season-ending surgery.

‘‘I could only imagine having to deal with something like that,’’ Cubs right-hander Kyle Hendricks said. ‘‘You know he’s been dealing with that for quite a while now. That’s the kind of guy that he is: He’s going to pitch if he can pitch, no matter what. That’s why he’s an unbelievable teammate. That’s why we love him.

‘‘But at the end of the day, he’s got to look out for himself at this point. You could see he just wasn’t right.’’

Big day for pen

Bullpen workhorse Steve Cishek rejoined the team after returning Saturday to Chicago for a cortisone shot in his inflamed left hip.

After throwing ‘‘free and easy’’ Wednesday, he’s scheduled for his first post-injury bullpen session Thursday. After that, a timetable for his return might be determined.

Might he be ready Tuesday — his first eligible day to come off the IL — against the Giants?

‘‘If we continue at this rate, yeah, I don’t see why not,’’ he said.

Closer Craig Kimbrel also will throw a bullpen session Thursday, his second since a sore right knee sidelined him last week. Kimbrel said his knee has responded well so far, and he and the team will determine a course of action if Thursday goes well.

Contreras update

Catcher Willson Contreras, who has been on the IL since injuring his hamstring Aug. 3, returned to Chicago to increase his rehab and strength work. He’s not expected back from the IL until next month.