He broke the bone in his hand diving head-first in Saturday's no-hitter.
The veteran first baseman's return this season seems less and less likely.
Espinosa has been dealing with the hamstring issue for some time and tests revealed that he has a minor strain.
"They want to see me come back healthy and they’ve seen firsthand what I can do healthy," he said.
Hurt obliques have cost Nationals' players significant time this season, but the first baseman is optimistic about his return.
The Nationals rookie center fielder can't get his knee to stop swelling, and Ryan Zimmerman and Yunel Escobar are out Wednesday, too.
Also: Stephen Strasburg will throw another bullpen session on Sunday before being cleared to start Wednesday.
Given the extent of damage to his right elbow, Barrett joked he was surprised he could throw the ball over the plate.
The right-hander had successful surgery on his right elbow Thursday, while the Nationals' rookie center fielder is out of the lineup again.
Harper left the game in the fourth inning with an injury, the team said.