Harden (9-9, 4.09 ERA) has not started since Sept. 16, when he went three innings in a loss to the Brewers at Wrigley Field. The Cubs have 11 games remaining.
"I'm not sure about Harden, I'm really not," Piniella said. "I'm not certain on whether Rich is going to get another start or not. It won't be this weekend in San Francisco."
The Cubs do have a doubleheader Sept. 30 against Pittsburgh, but may use the remaining games to look at some of the young pitchers on the roster such as Jeff Samardzija, who started Wednesday against the Brewers. Samardzija is expected to get another start during the Cubs' final homestand.
"All I know is the three starters I gave you for San Francisco, and Sunday is 'iffy,'" Piniella said of the upcoming four-game series against the Giants in which Ryan Dempster, Carlos Zambrano and Tom Gorzelanny will start.
Dempster (10-8, 3.72 ERA) was expected to start next Tuesday in an attempt to get closer to 200 innings for the season. He has 179 in 28 starts so far.
Ted Lilly (12-8, 3.02 ERA) is penciled in as Sunday's starter against the Giants. He's been slowed because of tendinitis in his left shoulder. Rookie Randy Wells (11-9, 3.00 ERA) had lobbied for more starts in the final games, and could go Sunday, Piniella said.
Harden moved to Arizona this past offseason so he could train with the Cubs' staff, including strength coach Tim Buss and athletic trainer Mark O'Neal, and made 26 starts this year.
"I've felt pretty good this season," Harden said. "I felt a little inconsistent at times. I would've liked to have pitched better some days. Overall, I was healthy and felt great. Hopefully, I can build on this in the offseason and come back stronger. We'll see what happens here."
The right-hander said if the Cubs were still competing for a postseason spot, there'd be no discussion regarding whether he'd be starting or not.
"I wish we were right in it this time of year," Harden said. "Then it's easy, I'm pitching no matter what. It's a little different now."
He is one of four free agents on the Cubs, joining Kevin Gregg, John Grabow and Reed Johnson.
"I'd like to [come back]," Harden said. "I have a lot of respect for [general manager] Jim Hendry and Lou and the coaching staff and trainers. It's been a good fit for me. We'll see and I'm sure we'll be talking about that in the next few weeks here."
Carrie Muskat is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.