Nationals general manager Mike Rizzo told Major League Baseball's official website (www.MLB.com) that the trade was a done deal but not expected to be approved by league offices until Saturday.
Guzman, an original member of the Nationals, goes from a last place team to the first place Rangers, who are running away with the American League West.
"We decided to move Cristian to the Rangers," Rizzo told MLB.com. "They needed an infielder.
"We have two good young Double-A prospects that will help our inventory - two starting candidates. It's a trade -- veteran player for prospects."
Guzman is batting .282 this season with two home runs and 25 RBIs.
(Writing by Steve Keating in Toronto, Editing by Steve Ginsburg)