The Colorado Rockies designated infielder Chris Nelson for assignment and selected the contract of infielder Nolan Arenado from Triple-A Colorado Springs on Sunday.
Nelson, 27, was batting .242 with no home runs and four RBI in 21 games this season.
Selected by the Rockies as the ninth overall pick in the 2004 First-Year Player Draft, Nelson has played 212 games with the Rockies over the last four seasons.
In 2012, he played a career-high 111 games, posting a .301 batting average with nine home runs and 53 RBI, but suffered a wrist injury early in the season and later experienced an irregular heartbeat.
Arenado, 22, has batted .364 with three home runs and a team-high 21 RBI in 18 games for Colorado Springs. He also has 11 doubles, which leads the Pacific Coast League.