The team announced Wednesday that Turner has a non-displaced fracture in his finger, the result of being hit by a pitch during a bunt attempt in the first inning of Tuesday's 8-2 loss to the Philadelphia Phillies.
"It's a big loss," Nationals manager Dave Martinez said via ESPN. "He's our starting shortstop. But we've got to keep going."
Last season, Turner appeared in all 162 games for the Nationals, hitting .271 with 19 homers and 73 runs batted in.
He led the National League in 2018 in games played, plate appearances and at-bats.
"It's never fun," Turner said Wednesday, according to MLB.com.
"Doesn't matter if it's the first game or the last game of the year -- injuries aren't fun. Takes you out of the lineup, takes you out of the game and you just want to be out there competing. Not fun, but it is what it is."
This season, Turner was off to another good start, hitting .357 (5-for-14) with three extra-base hits and four stolen bases.
With Turner out, the team recalled infielder Adrian Sanchez from Triple-A Fresno.