PHILADELPHIA -- Outfielder Jason Heyward is considered day to day after being scratched from the Cubs' lineup Wednesday due to left knee inflammation.

Heyward said he doesn't know exactly when he sustained the injury, but he felt pain for the first time when he got out of bed in the middle of the night following Tuesday's 4-2 loss to the Phillies.

"The situation was I tried to get out of bed, go to move my knee, and got a kind of locked-up feeling," Heyward said. "Sharp pain [in the] front of my knee. So I would go to extend it and bend it, and get a sharp pain like that. It's nothing ligament-wise, so just rest."

Heyward was actually encouraged by how the knee responded at the ballpark on Wednesday. He got the knee to loosen up and took some swings in the cage, during which the pain subsided for the most part. The concern was some of the discomfort returning as he cooled down between sessions.

"At first, I was like, 'There's no way [I can play],'" Heyward said. "Then I came in and started getting loose, and felt a lot better about it. Then I ended up saying, 'It's not going to be the best thing to do to go tonight.' Just because it's one thing to get it hot and loose, but when you start to calm down between innings and downtime and pounding on it and all that stuff, it's tough to [keep it loose]."

Although manager Joe Maddon was also encouraged by the way Heyward's knee responded pregame, the skipper opted to play it safe by putting Tony Kemp in the leadoff spot and moving Ian Happ to center field. Heyward may also get another day to rest on Thursday, with the Phillies scheduled to start left-hander Drew Smyly in the series finale.

"After Jason hit, he reported that it was still there, but not awful," Maddon said. "So we thought the best thing to do was to just back off today. We do see a lefty tomorrow in Smyly, so it may end up being two days, which would be fine with me, but we'll play it day by day. From what I've heard, it's nothing we should really be concerned about right now."

Heyward echoed that sentiment, adding that he does not anticipate this becoming anything that requires a stint on the injured list.

"No, it's not going to be an IL thing," Heyward said. "Sometimes you just need to stop to not make something worse."

Cishek, Kimbrel making progress
Right-hander Steve Cishek rejoined the Cubs in Philadelphia and did some pregame work on the field prior to Wednesday's game, including playing catch from approximately 45 feet.

Cishek, who was placed on the injured list Saturday with left hip inflammation, had previously returned to Chicago, where he received a cortisone shot for his ailing hip. He then rested for a few days to allow the treatment to set in before resuming baseball activities on Tuesday.

"It was pretty free and easy. I was getting after it pretty hard today," Cishek said. "I played light catch yesterday. The other three days, I took off. The ball is coming out good, so we're just going to keep progressing from here."

Cishek is expected to throw a bullpen session on Thursday, as is fellow reliever Craig Kimbrel (right knee inflammation). Kimbrel will be throwing his second bullpen session after going through one on Tuesday without any issues. The club will then determine the next step for Kimbrel, which could be either a rehab appearance or simply activating him from the injured list.

As for Cishek, the earliest he can return would be Tuesday's series opener against the Giants at Wrigley Field. Though he needs to see how the hip continues to respond to the increased work this week, Cishek is hopeful that he will indeed be activated as soon as he's eligible.

"I hope so. If we continue at this rate, yeah, I don't see why not," Cishek said. "But it also depends on how I feel, and what the expectations are for me. We haven't really gone that far yet. All I know is I throw a bullpen [Thursday], and then we'll go step by step from there."