Manager Davey Johnson said after tonight's game that the Nationals will place catcher Carlos Maldonado on the 15-day disabled list with a back injury and will call up outfielder/first baseman Tyler Moore from Triple-A Syracuse.
Maldonado said that he's having an issue with a muscle in the right side of his back, and described the injury as somewhat of a spasm.
He has played in four games since getting called up from Syracuse back on May 15, going hitless in nine at-bats with two walks and one RBI.
Moore started the season in Syracuse before being called up on April 29. He hit .158 (3-for-19) in 12 games during his first stint with the major league club and was optioned back to Triple-A on May 28.
Overall at Syracuse this season, Moore is hitting .310 with nine homers and 29 RBIs. He hit two home runs and drove in six in the six games with the Chiefs since being sent down a little over a week ago.
Johnson also announced that Mark DeRosa (oblique) will go on a rehab assignment either tomorrow or Friday. He'll likely report to Single-A Potomac.
Reliever Ryan Mattheus, meanwhile, will take part in pitchers' fielding practice tomorrow, and could throw a simulated game at Potomac on Friday. If all goes well with his injured left foot, he hopes to go on a rehab assignment over the weekend, and could rejoin the Nats next week.