The Washington Nationals placed right-handed reliever Ryan Madson (pectoral muscle strain) on the disabled list Sunday.
Nationals manager Davey Johnson said Madson will have an MRI on Monday. The move is retroactive to Thursday, and Johnson said it was "just to be safe."
Madson, 37, who appeared in 21 of the Nationals' first 42 games, was unavailable to pitch Saturday and Sunday.
He has a 4.19 ERA over 19u2153 innings this season. He has 20 strikeouts and six walks and has not allowed a home run this season.