CINCINNATI — Washington Nationals outfielder Elijah Dukes will be sidelined for four to six weeks because of a knee injury suffered during a 3-2 loss to the Cincinnati Reds on Saturday night.

Dukes tore cartilage and partially tore a tendon in his right knee when he slammed into the left-field wall after catching a flyball in the seventh inning. He grabbed his knee and was taken off the field on a cart.

Dukes will have surgery on Monday. The Nationals didn't immediately replace him on the roster.

The 23-year-old outfielder is batting .263 with six homers and 20 RBIs in 52 games. He will become the 15th Nationals player to go on the disabled list this season.