WASHINGTON -- Nationals reliever Ryan Mattheus threw off a mound on Friday for the first time since breaking his pitching hand, and manager Davey Johnson said the right-hander could begin a Minor League rehab assignment in about 10 days.
Mattheus suffered the injury on May 19 in San Diego, when he punched a locker after giving up five runs in an inning of work, by far his worst performance of the season. He already had been throwing off flat ground, and before Friday's series opener against the Padres, he made 25 tosses off the mound.
"Well, it's kind of ironic, here San Diego is, and this is the club that made him break his hand," Johnson said. "Now, he's back on the mound. I hope he doesn't run in after and start hitting his locker again.
"But he threw great. Everybody was impressed who saw him throw."
Mattheus will throw off a mound at least a couple more times, and assuming no problems arise, he then would face Nationals hitters during batting practice. If that goes well, he would go on a rehab assignment, although Johnson doesn't think he would need much time.
"His main pitch is his sinker, and his arm strength is pretty good now," Johnson said. "He just has to build up some endurance in that shoulder."
Mattheus has been an important piece of the Nationals' bullpen. Before that outing in San Diego, he had a 2.35 ERA in 15 1/3 innings. In 115 career appearances, the 29-year-old owns a 3.14 ERA.
Andrew Simon is a reporter for MLB.com. Follow him on Twitter @HitTheCutoff. This story was not subject to the approval of Major League Baseball or its clubs.