SAN FRANCISCO -- Alfonso Soriano is ahead of schedule in his rehab, but the Cubs are going to be very careful before activating the left fielder from the disabled list.

Soriano, sidelined since Aug. 5 with a strained right quad, impressed Cubs manager Lou Piniella with his agility and mobility during a workout on Wednesday. The projected return date is Sept. 1, but that could change.

"Soriano looked good, and he's amazing," Piniella said Thursday. "If you see him running around out there, you think he's one of your regulars instead of somebody on the [disabled list]. We've got to be very careful, because one more problem and he's out for the year.

"We'll be as cautious as we can," Piniella said. "We're not going to rush this thing to the point where by rushing it, he can sustain an injury."

Soriano took batting practice for the first time on the field Wednesday and will hit again Friday in Arizona.

"I still cling to the first of September [return date], like we've talked about it," Piniella said. "It did surprise me how much work he could do."

At one point during batting practice, Soriano was able to jump over a batted ball as he ran the bases.

"I couldn't do that when I was feeling good," Piniella said.

Athletic trainer Mark O'Neal and the Cubs medical staff will have to make the final decision.

"We want to do what's right for him and what's right for the baseball team," Piniella said of the outfielder, who was hitting .297 with 18 homers and 42 RBIs. "I know this, if he has a re-occurrence because we bring him back too soon, we're the ones who will pay the penalty for it."

Soriano has been a good cheerleader during his stint on the DL.

"He's about 10 days ahead of schedule of where we thought he would be," Piniella said.

Ask Soriano, and he wants to be ready for the Cubs' showdown next week with the Milwaukee Brewers.

"I'm not going to rule it out," Piniella said, "but let's see what happens here in Arizona. He's going to get a lot of steady work, and we'll see how he feels.

"I'd like [to have him back then]," Piniella said, "but after the Brewers series, we still have 30 games."

Roster moves: The Cubs acquired outfielder Craig Monroe from Detroit for a player to be named, which will be decided after the regular season ends. Monroe will join the Cubs in Arizona this weekend.

The Cubs aren't done tinkering. They are looking for an experienced pitcher who could provide long relief help.

Teams need to have their 25-man roster set by Aug. 31, although there is some wiggle room. If a player is on the disabled list on that date, he can be added.

"We're getting close," Piniella said. "I think you might see us add one more piece and that's the end of it."

As far as September callups are concerned, the Cubs could add six players for the stretch. Among the candidates are catcher Geovany Soto, infielder Ronny Cedeno and pitcher Will Ohman.

"They will be people we're going to be able to use," Piniella said. "If we're not going to use them, we don't want to clutter up the roster. It's basically the same guys who have been here. I don't think we'll add to that list."

About last night: In case you didn't stay up late to watch, Rich Hill posted his 14th quality start of the season Wednesday night against the Giants but didn't get the win. He also struck out 10, the fifth time in his career he's reached double digits in strikeouts. He also fanned 11 June 7 against Atlanta this year.

What was working?

"The curveball for strikes, and being consistent with the fastball and continuing on the same aggressive mindset and taking it out there for the seven innings," Hill said. "I just tried to stay consistent with what I was doing."

"He was impressive," Cubs catcher Jason Kendall said. "He settled down and could throw his curveball whenever he wanted to and spotted his fastball and got in a groove."

Hill admitted it's fun to face players like the Giants' Barry Zito and Barry Bonds.

"I look at it from the point that this is a guy you watched pitch as you come up pitching in college and in the Minor Leagues," Hill said of Zito. "He's got the big curveball, and it's a lot of fun to watch him pitch."

He shrugs off his personal win-loss record.

"Personal goals aren't what you look for," Hill said. "When it's all said and done at the end, it's not what you did during the season, it's how the team did. It's a positive way of looking at it."

Extra bases: The Cubs have challenged Bonds for the most part in this series but did intentionally walk the slugger in the eighth Wednesday. "I told Barry when I walked by him, 'You're just too good,'" Piniella said. "He smiled." ... Bob Howry has gotten a little breather and hasn't pitched since Saturday. "I told him his vacation is over," Piniella said. ... Cubs coach Mike Quade was waiting for Jake Fox as he came off the field Wednesday after scrambling to get a ball off the wall. "He said, 'You did exactly what you're supposed to do, and all you need to do is be in a better position to react,'" Fox said. The rookie has gotten a lot of advice on this callup from veterans like Daryle Ward and Henry Blanco. ... Blanco's pinch-hit at-bat Wednesday was his first Major League action since May 30. ... Tickets go on sale Friday for the Sept. 10 makeup game between the Cubs and St. Louis Cardinals.

Minor matters: J.R. Mathes gave up three runs on seven hits over six innings in Triple-A Iowa's 4-3, 10-inning loss to New Orleans on Wednesday. ... Donnie Veal gave up one earned run on four hits over five innings in Double-A Tennessee's 3-1 loss to Mobile. ... Steve Clevenger had four hits and Brian Dopirak had three with three RBIs in Class A Daytona's 6-5 loss to Jupiter. ... Jeremy Papelbon threw seven shutout innings in Class A Peoria's 8-0 win over Wisconsin.

On deck: Lefty Sean Marshall will open the Cubs' three-game series at Arizona opposite Micah Owings (6-6, 4.70 ERA) on Friday. Marshall (6-6, 4.21) is coming off a win over the Cardinals. First pitch is scheduled for 8:40 p.m. CT, and the game will be broadcast on Comcast Sports Net.