Updated at 5:25 p.m.
The Nationals have purchased the contract of Ryan Mattheus from Class AAA Syracuse and have placed fellow reliever Cole Kimball on the 15-day disabled list with right shoulder inflammation.
It's unclear how severe Kimball's injury is or when it occurred, but the rookie right-hander entered with the bases loaded in the sixth inning of last night's loss in San Diego and immediately walked pinch-hitter Kyle Phillips on five pitches to force in a run. He wound up facing two more Padres batters and induced flyouts from each before departing.
Kimball, 25, has impressed overall since his promotion, posting a 1.93 ERA in 12 relief appearances, though he has issued 11 walks in 14 innings.
Mattheus wasn't much on the club's radar during spring training, but the right-hander quickly thrust himself into the mix once the season began, going a combined 2-1 with a 1.46 ERA in 22 appearances between Syracuse and Class AA Harrisburg. He did not allow a run in 10 innings at Class AAA.
The 27-year-old was acquired from the Rockies in July 2009 in a trade that sent veteran Joe Beimel to Colorado, but he missed most of 2010 following Tommy John surgery. Mattheus was not on the Nationals' 40-man roster, but the club had an open slot to add him today.
Meanwhile, Ryan Zimmerman will continue his rehab assignment tomorrow at Syracuse after playing one game at low-Class A Hagerstown and three games at high-Class A Potomac. Zimmerman, who is not playing today, is likely to be activated off the DL when the Nationals begin a homestand Tuesday against the Cardinals.