With one out, Sanchez walked Brandon Nimmo. Immediately after the pitch, the team's medical staff visited Sanchez on the mound. Following a brief consultation, the veteran righty yelled into his glove and then walked gingerly back to the dugout.
Martinez said after the game that the 35-year old Sanchez had a hamstring strain, will have an MRI on Friday and likely will wind up on the injured list.
"He tried to walk it off, thinking it was a cramp, but it pulled on him pretty good," Martinez said. "He's dealt with it. He knows he's dealt with it before. He doesn't think this one is really bad. But the MRI will tell us more tomorrow."
Sanchez, who has a 5.10 ERA and is winless in nine starts this season, had two strikeouts and had allowed one hit prior to exiting with a 4-0 lead.
"I'm probably going to miss another start, but I don't know yet," Sanchez said. "I just want to wait for tomorrow. I just got a little twist and after, it's really hard for me to hold my body straight to home plate. I tried to keep it as soft as I can, just to not put too much pressure on my leg, but it's my landing leg. There's nothing I can do. If I've got a leg problem, I can't even throw the ball straight to home plate."
The Nationals are one of three teams that have used only five starting pitchers this season, along with the Cincinnati Reds and Miami Marlins. If Sanchez misses his next start, his probable replacement would be Fedde, a former first-round pick who has started 14 games for the Nationals over the last two seasons.
Sanchez signed a two-year, $19 million with the Nationals as a free agent in December. He went 7-6 with a 2.83 ERA in 24 starts for the Atlanta Braves in 2018.