Nats activate reliever Ryan Mattheus
Mattheus, who missed the last 58 games with a fractured right hand, has a 4.96 ERA in 14 relief appearances this season.
In six appearances during a rehab assignment, he had a 2.25 ERA pitching for the Gulf Coast League Nationals, Single-A Hagerstown, Double-A Harrisburg and Triple-A Syracuse.
Because teams are permitted to add a player for doubleheaders, the Nationals won't have to make a corresponding roster move until after Friday's games.
Washington manager Davey Johnson said Friday morning that reliever Drew Storen has the flu and was likely unavailable for the doubleheader.
Copyright 2013 by The Associated Press
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