Associated Press

Outfielder Marlon Byrd was suspended 50 games by Major League Baseball on Monday after testing positive for a performance-enhancing substance.

Major League Baseball said the 34-year-old Byrd tested positive for Tamoxifen, which can reduce side effects of steroid use and increase testosterone. It is often used to treat breast cancer patients.

“I made an inexcusable mistake,” Byrd said in a statement released by the players’ association. “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.”

Byrd is currently a free agent, and will be placed on the restricted list for the duration of his suspension, which began immediately.

He started the season with the Cubs and was dealt to the Red Sox on April 21. He was designated for assignment by Boston on June 9 and released four days later.

Mets’ Parnell to replace closer

New York Mets manager Terry Collins says right-hander Bobby Parnell will serve as the team’s closer while Frank Francisco is on the 15-day disabled list with a left oblique strain. Parnell is 1-1 with 15 holds and a 3.19 ERA in 36 appearances this season.

Rangers’ Holland sent down

Texas Rangers left-hander Derek Holland is going to Triple-A Round Rock for two rehabilitation starts. The Rangers say Holland will be assigned to the Express on Wednesday, when he will throw about 50 pitches in a start.

Cubs’ prospect Rizzo to debut

Cubs prospect Anthony Rizzo is Chicago-bound and could get his first start as early as today.

The 6-foot-3 first baseman was hitting .342 with 23 home runs and 62 RBI for Iowa.

Rockies demote starter White

The Colorado Rockies have optioned struggling right-hander Alex White to Triple-A Colorado Springs, one day after his third consecutive poor start.

White was 2-6 with a 6.45 ERA in 10 starts since he was recalled May 8.

Nationals’ Nady out 15 days

The Washington Nationals have placed outfielder Xavier Nady on the 15-day disabled list Monday with a tendinitis in his right wrist.

Nady was batting .157 with three home runs and six RBI.