The Nationals have added a pitcher to their roster at the expense of another. As first reported by Craig Heist of WTOP Radio, right-handed reliever Ryan Mattheus has been placed on the disabled list with plantar fasciitis.

The #Nats will put Ryan Mattheus on the DL with plantar Fasciitis and reinstate Chien-Ming Wang from the DL according to a baseball source.

— Craig Heist (@cheistWTOP) May 22, 2012

Federal Baseball has more:

Mattheus told reporters on Monday that he'd felt discomfort in his left foot while running at Citizens Bank Park before [Monday night's] game against the Philadelphia Phillies. The foot was reportedly bothering Mattheus for several weeks.

The injury is another blow to the Nationals bullpen, which had benefitted from Mattheus' solid performances. The 28-year-old right-hander had gone 2-1 with a 2.25 ERA and a WHIP of 1.300 in 20 innings pitched.

For his part, Wang has made a total of five starts at Potomac (high-A), Hagerstown (A), and Syracuse (AAA). In those starts, Wang posted a 3-0 record with an ERA of 3.52 and a WHIP of 1.272 in 30.2 innings pitched. Nationals manager Davey Johnson has said he will place the Taiwanese pitcher in the bullpen.

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