(Reuters) - The front-running Los Angeles Dodgers suffered a setback on Thursday when they placed slugging outfielder Matt Kemp back on the 15-day disabled list with a strained left hamstring.

Kemp, who last year led the National League with 39 home runs and 126 runs batted in while hitting for a .324 average, had played just two games after missing 14 games with the same injury.

This season, Kemp had blasted 12 home runs in 36 games played and was batting .355.

The Dodgers, whose 32-18 record is the best mark in Major League Baseball, called up infielder/outfielder Alex Castellanos from Triple-A Albuquerque to take Kemp's spot on the roster.

Castellanos, making his first appearance in the major leagues, was hitting .379 with 10 doubles, four triples, five homers and 14 RBIs in 22 games with Albuquerque.

(Reporting by Larry Fine in New York; Editing by Frank Pingue)