Per Jorge Castillo of the Washington Post, Nationals manager Dave Martinez confirmed Kendrick's injury and announced he would undergo surgery on Monday.
Per Byron Kerr of MASN Sports, the Nationals are expected to call up top prospect Juan Soto with a spot opening up on the 25-man roster.
Kendrick was injured during the eighth inning of the first game of a doubleheader against the Los Angeles Dodgers on Saturday. He was carted off the field after making a catch in the outfield when his leg appeared to give out.
"All he said was he stepped down and he felt something," Martinez told reporters after the game. "We told him to just stay down."
Kendrick appeared in 40 games for the Nationals in 2018. The 34-year-old leads the team with a .302 batting average.
Soto, 19, has had a meteoric rise through Washington's system in 2018. He started the year in Low-A with Hagerstown and was promoted to Double-A last week with a .362/.462/.757 slash line and 14 homers in 39 games.
The Nationals (24-20) are three games behind the Atlanta Braves in the National League East after being swept in their doubleheader against the Dodgers.