But the switch-hitting outfielder reported feeling better on Thursday and did some light work after getting more treatment. He is scheduled to test the calf running when the Cubs get to Cincinnati on Friday.
"We're not going to DL him," Piniella said. "We feel, and he feels, that he is going to be available to pinch-hit by the time we get to Cincinnati and that there is a good probability that he can play in Houston."
The Cubs will be in Cincinnati for three games this weekend, then go to Houston to conclude the road trip with three more games beginning on Tuesday.
After a successful bullpen session on Thursday, Harden is scheduled to come off the DL when the Cubs get back to Chicago and start next Friday's homestand opener against Minnesota.
Harden with make one Minor League rehab start, pitching for Iowa against Round Rock in a Triple-A Pacific Coast League game on Sunday. He is slated to work five innings and throw about 75 pitches.
Harden, who is 4-2 with a 4.74 ERA in eight starts, strained his back pitching against Houston on May 17 and went on the 15-day DL when he wasn't able to make his next start.
The right-hander threw off the mound for the first time on Tuesday and said that he felt no discomfort.
"It was good again. No problem," Harden said after his second bullpen session on Thursday at Turner Field.
When Harden returns to the rotation, Sean Marshall will go to the bullpen. The left-hander is 3-4 with a 4.73 ERA in 11 appearances, three in relief. He will make his ninth start on Saturday in Cincinnati.
The Cubs are counting on Bradley be able to be available by then.
"I would need him at least to be able to pinch-hit those days in Cincinnati," Piniella said. "Then, when we go to Houston, we'll see how he is. If he's ready to play, we'll put him out in right field."
Bradley had to leave Tuesday night's game after coming up lame running hard to first base in the fourth inning on a grounder to second baseman Kelly Johnson. An MRI performed on Wednesday confirmed that he had a strain, although not a severe one.
This has been a difficult season for Bradley, who signed a three-year, $30 million deal with the Cubs as a free agent during the winter.
He was bothered by a sore quad during Spring Training and had a groin strain in April. He has played in 39 games, batting .220 with five homers and 14 RBIs.
"We need him on the roster playing," Piniella said.