Jose Acosta of the Pirates' Venezuelan Summer League affiliate, and free agent Jorge Castillo were also suspended. All four players will miss 50 games.
Lopez tested positive for Formestane, an "estrogen control agent" that reduces excess estrogen and helps build lean muscle and strength. The 26-year-old shortstop, currently with Triple-A Syracuse, the Nationals' top affiliate, spent parts of two seasons in the Majors, most recently in 2007 with Cincinnati.
The Moca, Dominican Republic native was batting .216 with a homer and 11 RBIs in 58 games with the Chiefs after hitting .174 in 24 starts with Double-A Harrisburg. He originally signed with the White Sox in 2000 and made his Major League debut with Chicago in 2005 before bouncing around the Minors with the Reds, Blue Jays, Pirates and Nats.
Nicolas' suspension comes one day after he was promoted to Triple-A by the Tigers. The 28-year old, who tested positive for an amphetamine while with Double-A Erie, was promoted to Triple-A Toledo on Monday but has not appeared in a game. The D-backs' 2004 fifth-round pick out of Vanderbilt was hitting .279 with seven long balls and 38 RBIs in 70 games for the SeaWolves.
Castillo, 23, was the White Sox's 26th-round selection out of Florida International in 2008 after previously leading Louisville to the College World Series. The Miami native spent three seasons in Chicago's system, including a huge rookie campaign when he batted .373 but was released from Class A Kannapolis on April 29 when he was hitting .244 with three RBIs in a dozen games. He'll serve his suspension upon signing with a new organization.
Acosta, 18, had appeared in one game for the Pirates' VSL club.
The Office of the Commissioner has suspended 64 Minor Leaguers this season, including 25 in the span of less than two weeks following Tuesday's announcement. Major League Baseball also recently announced increased efforts to eliminate human growth hormone from the game with random blood testing in the Minors.
There have been a string of suspensions handed out by the Commissioners office in the last two weeks, including:
- Former Nationals third-round pick Steve Souza and Class A Hagerstown teammate J.R. Higley were among four players suspended for using performance-enhancing drugs on July 15.
- Retired Triple-A outfielder Jon Weber and two others were suspended on July 19.
- Rangers prospect Cristian Santana was suspended after testing positive for Formestane on July 20.
- A pair of Dominican pitchers tested positive for performance enhancers on July 21.
- Five more Dominican Minor Leaguers were suspended on July 23, a day after MLB announced its new blood-testing program.
- Dodgers outfielder Prentice Redman was among six players suspended on July 26. Redman, who tested positive on June 25, was banned an additional 100 games following his second positive test.