Ramos will be Washington's backup catcher until Nieves returns to the team on Friday against the Phillies. Manager Jim Riggleman didn't rule out Ramos starting against the Braves on Thursday.
Ramos will be sent back to Syracuse once Nieves returns, but will get a September callup.
Ramos was acquired from the Twins for reliever Matt Capps on July 29. Since the trade, Ramos has been productive, hitting .317 with two home runs and six RBIs for the Chiefs.
The Nationals are hoping to have Ramos, 23, for a long time, as he is a highly regarded prospect. He made his Major League debut this year for Minnesota and was 8-for-27 (.296) with an RBI.
Before the trade to Washington, Ramos was playing for Triple-A Rochester, hitting .241 with five home runs and 30 RBIs.
"My first time in the big leagues, I was very excited," Ramos said. "In my first game, I went 4-for-5. The second one, I went 3-for-4. When Minnesota sent me to Triple-A, I was a little bit down because I know I can play in the big leagues. When I was traded, I was excited because I know I have more of an opportunity. I'm going to play hard here and see what happens."
While he is with the team, Ramos hopes to learn a lot from starting catcher Ivan Rodriguez, his boyhood hero.
"Right now, there is an opportunity to learn from him and talk a lot to him," Ramos said.
The Nationals were in need of catching depth because Jesus Flores has missed the entire season with a right shoulder injury. There isn't a timetable on when he will return to the big leagues. Flores has dealt with the injury since May 2009 -- when he was hit by a foul tip off the bat of D-backs outfielder Chris Young.
Washington's other top catching prospect, Derek Norris, has also missed a lot of time because of injuries. He still needs to work on his game behind the plate.