Kendrick, 33, said he injured himself Saturday throwing a ball from the outfield at Nationals Park. He is hitting .333 with four doubles, one triple, five RBIs and an .883 OPS in 10 games.
Kendrick has not played since Saturday, so he could be activated as early as April 26.
"It's like upper abdomen, lower rib cage," Kendrick said. "Hopefully it's something that's not a nuisance, but we'll see. It hasn't gotten any worse over the past couple days, so hopefully it's something that'll be done pretty quickly."
Leiter, 26, allowed one run and struck out 11 in 5 1/3 innings with Triple-A Lehigh Valley.