It was later announced that Wang had suffered a strained left hamstring on the play. Wang later went to the hospital for further tests.
With no score between the two clubs and one out, Yankees catcher Russell Martin hit a soft ground ball toward first. Wang fielded the ball and fell down awkwardly after an initial misstep before colliding with Martin coming across the base.
"I could tell right away that when he got up and he was limping, that was it for him," manager Davey Johnson said. "I hope it's not serious. He is throwing the ball exceptionally well. I'm really pleased with what I'm seeing. It just reaffirms the fact that he is back. It's really a tough break to see it happen.
"Obviously, I can tell and you can tell right away he kind of hyperextended that left hammy. ... He was throwing the heck out of the ball. He was pitching 90, 91 [mph]. We hope he has a great spring."
First baseman Chad Tracy said that Wang did nothing wrong in terms of trying to make the play on an in-between hop. Tracy said he saw Wang roll his left ankle before hurting the hamstring.
"When I saw him, I saw him roll his ankle first," Tracy said. "And then make his next try, it looked like he hyperextended something. It happened real fast. It didn't look natural. It was one of those in-betweeners. He was going to take the ball to the bag. I was there in case [the ball] got by. It's one of those things you work on during Spring Training all the time. It's not really how you draw that one up."
The injury comes at a bad time. Wang has been projected to become the fifth starter in Washington's rotation, while the team was thinking about trading left-hander John Lannan, who allowed four earned runs in four innings against the Yankees.
If Wang is not ready for Opening Day, Lannan more than likely will become the fifth starter.
Wang is trying to return to full strength after missing a lot of time over the past few years. He had a serious foot injury in 2008, and a shoulder injury suffered in 2009 sidelined him for close to two years.
Prior to Wang's injury on Thursday, Yankees manager Joe Girardi was not surprised to see Wang recover from his injuries.
"He went through some serious injuries that he had to deal with," Girardi said. "We've always pulled for him, because he's such a good guy and he meant a lot to our organization. I think all of us have kind of kept check on how he's doing.
"I'm not surprised [he's doing well]. You could see how much he loved to compete and loved to pitch. He was a young man and he wanted to get back at it. [The shoulder] is a tough injury to come back from, but he's worked hard at it.
Wang's pitching line Thursday for his first action against his former team finished at 2 2/3 shutout innings pitched, with two hits and four strikeouts.
Bill Ladson is a reporter for MLB.com and writes an MLBlog, All Nats All the time. He also could be found on Twitter @WashingNats. This story was not subject to the approval of Major League Baseball or its clubs.