CHICAGO -- Bryan LaHair has been aware of Anthony Rizzo since Spring Training when the two were lockered next to each other in the Cubs' clubhouse.

On Tuesday, LaHair will have to step aside to make room for Rizzo, who is taking over as the Cubs' everyday first baseman.

"It is what it is," LaHair said Monday. "He'll get the opportunity to play. He's a first baseman and that's the only position he plays. He's got a big bat, so we have to have him. I'm comfortable in the outfield and I just want to hit. As long as I'm in the lineup, I don't really care [where I play]."

LaHair has kept an eye on Rizzo's stats at Triple-A Iowa. Last year, LaHair led the Pacific Coast League with 38 home runs. Rizzo has hit 23 in 60 games with Iowa. But the two haven't kept in touch via text messages or phone calls.

"I'm up here playing first, he's down there playing first," said LaHair, who has started 50 games at first, but has been lifted against left-handed pitchers. "When he gets here, we'll mesh well and help each other out."

LaHair said Carlos Pena helped him last year when he was called up to the Cubs in September. He'll do the same for the 22-year-old infielder.

"We're teammates, friends, and we'll try to help each other out," LaHair said.

Former Cub Byrd suspended for failed drug test

CHICAGO -- Former Cubs outfielder Marlon Byrd has received a 50-game suspension after testing positive for Tamoxifen, a performance-enhancing substance, which is in violation of Major League Baseball's Joint Drug Prevention and Treatment Program.

Byrd, who is a free agent, will be placed on the restricted list for the duration of his suspension.

"I made an inexcusable mistake," Byrd said in a statement. "Several years ago, I had surgery for a condition that was private and unrelated to baseball. Last winter, I suffered a recurrence of that condition and I was provided with a medication that resulted in my positive test. Although that medication is on the banned list, I absolutely did not use it for performance enhancement reasons.

"I am mortified by my carelessness and I apologize to everyone who loves this game as I do," he said. "I will serve my suspension, continue to work hard and hope that I am given an opportunity to help a club win later this season."

Cubs players were surprised at the news.

"I'm surprised and feel bad for him because he was a great teammate," Alfonso Soriano said. "I feel sad when you hear names and drug tests, no matter who's the guy, whether he's a bad or good teammate, you feel bad because he's part of the family."

The Cubs traded Byrd to the Red Sox on April 21 for reliever Michael Bowden, and the outfielder was released on June 12. Will it be tough for him to come back?

"Especially after getting released and now getting the [positive] drug test, it'll be a little difficult," Soriano said. "Who knows?"

Extra bases

• Cubs pitcher Ryan Dempster, on the disabled list with a sore right lat, was able to throw on flat ground Monday, the first time he's done so since he was sidelined June 16, and reported no discomfort. However, Dempster was expected to miss at least two more starts.

"Everything went really well," Cubs manager Dale Sveum said Monday.

Third baseman Ian Stewart, on the disabled list since June 13 with soreness in his left wrist, was able to hit Monday and was making progress, Sveum said. There is no timetable for his return.

• While Sveum has kept an eye on Anthony Rizzo, who will be promoted Tuesday from Triple-A Iowa, he's also been watching highly touted prospect Brett Jackson. The outfielder was batting .256 in 73 games with 16 doubles, nine triples and 11 home runs, but also has struck out 107 times.

"The strikeouts are at an incredible rate, which is a little strange," Sveum said. "It's the pitch selection as much as anything -- I think he went through a period where even the fastball was giving him trouble. Now it's the soft stuff, stuff that's hitting the earth, he can't seem to lay off either. He's got some strange stats. He's got an .850 OPS and has struck out over 100 times is a very strange stat in that category unless you're Adam Dunn."