Left-hander Matt Purke was placed on the seven-day disabled list prior to Wednesday's game due to shoulder stiffness, according to a club source.
The Hagerstown southpaw has made three starts, going 0-2 with a 5.87 ERA. He has struck out 14 and walked 12, surrendering one homer.
The Nationals' No. 2 prospect spent the first two months of the season in extended spring training, working to build strength and lengthen out his innings following shoulder inflammation.
Purke told me last week that he was making progress in his first two weeks with the Suns.
"It is not uncommon for pitchers to have to go through (extended spring training)," Purke said. "I am enjoying it and having fun and really working hard each day to get better and back to the form I have been working towards my whole life.
"I am still building. Basically, like I had to do two spring trainings with the time I had to take off. I am really coming out of that shell and getting my feet wet in regular season baseball. It is coming along. I am excited about it. As each day goes by, I get a little sharper and a little crisper."
Purke went through shoulder issues with Texas Christian and now must get rest and rehab from this week's setback.