CHICAGO -- With the Astros scheduled to start left-handers Saturday and Sunday against the Cubs, Anthony Rizzo will be in the Cubs' lineup both days, while Bryan LaHair may get a rare start against a southpaw.

"[Rizzo] is our third hitter, and I don't see me changing that in the future," Cubs manager Dale Sveum said Friday.

Rizzo possesses all the qualities the Cubs have been looking for in that spot, including someone who can deliver with runners on, whether it's moving them over or driving them in.

"You want a solid guy who can do a lot of things," Sveum said. "Obviously, home runs are nice, average is nice, but those key RBIs in the first inning are the biggest of all."

LaHair, who has moved to the outfield now that Rizzo has taken over at first base, is 3-for-35 with one home run against lefties this season, but left-handed hitters are batting .275 against J.A. Happ and .258 against Wandy Rodriguez.

"I'm thinking about it," Sveum said about starting LaHair against lefties Happ and Rodriguez. "We have to see some results. Unfortunately, the results are not real competitive. You do also need to give him a chance once in a while, especially against left-handers who have left-handed numbers that aren't very good."

Dempster improving, but won't return before break

CHICAGO -- Cubs pitcher Ryan Dempster played catch Friday and could throw off the mound Saturday or Sunday, but he will not be ready until sometime after the All-Star break.

Dempster, on the disabled list since June 16 with a sore right lat, said Friday he's making progress.

"It won't take me long once I get going," Dempster said. "I haven't said [I'm returning on] 'This date' because if I feel good, it could be sooner than that. I'm completely pain free. I just don't know how I'm going to feel throwing."

Randy Wells subbed for Dempster for two starts, but he was designated for assignment on Wednesday. The Cubs need another starter Tuesday against the Braves, and manager Dale Sveum said the options include Casey Coleman, who is currently in the bullpen, and Chris Volstad, who is pitching for Triple-A Iowa.

Volstad was sent to Iowa after opening the season 0-6 with a 7.46 ERA in eight starts with the Cubs. In eight starts at Iowa, Volstad is 2-3 with a 4.44 ERA, giving up 25 earned runs on 59 hits and 12 walks while striking out 41 over 50 2/3 innings.

Coleman was starting at Iowa at the beginning of the year but has been used strictly out of the bullpen with the big league team. On Wednesday, he gave up seven runs on six hits over 1 2/3 innings in relief.

The good news for the Cubs is that Dempster is indeed close to returning. The right-hander was 3-3 with a 2.11 ERA in 12 starts before he got injured, and he had not given up an earned run over 22 innings while winning his past three starts.

"Everything's been on schedule as far as what we're trying to do," Sveum said of Dempster. "Obviously, there's no timetable for anything yet."

Castro in mix for second straight All-Star Game

CHICAGO -- Starlin Castro will find out Sunday whether he will represent the Cubs at the All-Star Game for the second straight year.

"I think Castro is one of the young players who come around once in a while, and they can be as good as they want to be," Cubs manager Dale Sveum said Friday about the 22-year-old shortstop.

"The ceiling is very high, but it's still up to those individuals to make a difference on an everyday basis -- and not just as a hitter, but as a player and a winning hitter, and always making a difference in a ballgame to win ballgames."

Castro leads all National League shortstops with 93 hits and a .301 batting average, and his .437 slugging percentage ranks third. The Cardinals' Rafael Furcal led the latest All-Star voting results at shortstop, while Castro ranked third.

All season, Sveum has asked Castro to grade himself on a scale of one to 10 each day.

"He doesn't have a 10, but at least he's been good in games for the most part," Sveum said.

If NL All-Star manager Tony La Russa needed any recommendations, Sveum said he'd include outfielder Alfonso Soriano, who has 14 home runs in his past 40 games, starting May 15. That's the most in the NL and third most in baseball.

One of the Cubs' best options would have been Ryan Dempster, who is currently on the disabled list.

"He would've been a no-brainer if healthy the whole time," Sveum said of the right-hander, who has a 2.11 ERA in 12 starts.

The All-Star Game will be played in Kansas City on July 10 and can be seen on FOX at 8 p.m. ET.

Extra bases

• Third baseman Ian Stewart, who received a cortisone shot last week in his left wrist, is not making progress in his rehab.

"The shots and everything don't seem to be making a difference," Cubs manager Dale Sveum said. "I don't know what we'll end up doing with that. There's definitely no progress going on."

Stewart has been sidelined since June 13.

• Michael Brenly, son of Cubs television analyst Bob Brenly, hit his third homer and Nelson Perez hit his second in Double-A Tennessee's 13-6 loss to Birmingham on Thursday. Jae-Hoon Ha, who will play in the All-Star Futures Game, had two hits and is batting .253.

Jacob Rogers went 4-for-4 with two home runs in Mesa's 11-2 win over the D-backs in Rookie League action.

• Randy Wells, designated for assignment on Wednesday, has cleared waivers and been outrighted to Triple-A Iowa. Wells will join the Iowa Cubs' rotation. Wells was 1-2 with a 5.34 ERA in 12 games with the Cubs, including four starts. As a starter, he was 0-2 with a 7.04 ERA.