Outfielder Marlon Byrd, who admitted to working with the man whose center triggered a federal investigation of steroids use and distribution among athletes, has tested positive for performance-enhancing drugs.
The league announced on Monday that the free agent has received a 50-game suspension after testing positive for Tamoxifen. He will be put on the restricted list and will remain there until Aug. 20.
Tamoxifen -- its brand name in the United States is Nolvadex -- is a medicine that blocks the effects of the estrogen hormone in the body. It is used to treat breast cancer in women or men and is used by steroid users to prevent the growth of breast tissues in men and to stop post-cycle crashes.
Byrd issued a statement through the Major League Baseball Players Association Monday.
"I made an inexcusable mistake," the statement said. "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. 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."
Byrd 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.
Red Sox general manager Ben Cherington was asked if Byrd had failed any drug tests while with Boston. He said: "Not to my knowledge."
Red Sox manager Bobby Valentine was surprised as well.
"He played here and he played well," Valentine said. "I had no indication or I don't think anyone did."
While with the Cubs in spring training, Byrd admitted that he was the only player in baseball who still worked with Victor Conte. Conte's Bay Area Laboratory Co-Operative was at the center of the steroid scandal surrounding Barry Bonds, among others.
Byrd, however, insisted that he wasn't breaking any rules. He did say that commissioner Bud Selig had asked him to sever ties with Conte.
"[The pressure from MLB] does bother me sometimes," Byrd said to ESPNChicago.com in spring training. "But I think there should be pressure on everybody.
"I'm always going to watch what I take. I'm not going to say I have a bull's-eye on my back, but I think a lot of people are waiting for me to get my first positive test and miss 50 games. They'd like that just so they can say, 'We told you so.' I know that won't happen. I know I'm clean. I know the supplements I take are clean. I'm going to make sure of that."
On Monday, a post on Conte's Twitter account said he had nothing to do with the positive test.
"I did not give Marlon Byrd tamoxifen or provide him with consultation regarding his use of this drug," the tweet read.
Byrd is a career .278 hitter with 82 homers and 445 RBIs over 11 seasons with the Phillies, Nationals, Rangers, Cubs and Red Sox.
He hit .210 in 47 games with the two teams this year, though he hit .270 with a homer and seven RBIs in 34 games with Boston. The Red Sox picked him up when they had a shortage in the outfield after a rash of injuries.
"It's just unfortunate that it's another notch in baseball's belt as far as the drug policy and steroids has to do with the game" Cubs manager Dale Sveum said. "It's unfortunate those things keep happening."
Byrd finished fourth in the National League Rookie of the Year voting in 2003 with the Phillies and was a National League All-Star with the Cubs in 2010.
Information from ESPNBoston.com's Gordon Edes, ESPNChicago.com's Bruce Levine and The Associated Press was used in this report.