Matt Kemp (hamstring) back on DL

LOS ANGELES -- As expected, the Los Angeles Dodgers placed Matt Kemp on the 15-day disabled list Thursday, and the All-Star outfielder is expected to miss at least four weeks, according to team trainer Sue Falsone.

Kemp aggravated his left hamstring Wednesday night, just two days after he came off the DL following a two-week stint there with a strain of the same muscle.

To fill Kemp's roster spot, the Dodgers called up infielder-outfielder Alex Castellanos -- whom they acquired from the St. Louis Cardinals in last year's trade-deadline deal for shortstop Rafael Furcal -- from Triple-A Albuquerque.

Kemp aggravated the hamstring rounding third base as he scored from first on a first-inning double by teammate Andre Ethier on Wednesday.

"He has a little bit of swelling in the same area as well as a new strain in a different (higher) part of the hamstring," Falsone said. "They are both Grade 1 strains, but having two strains in the same muscle obviously means it's going to be a little bit longer from a rehabilitation standpoint. We're just going to take it day by day."

The injury happened again despite what appeared to be every possible precaution by the Dodgers' medical staff, including a two-game rehabilitation stint for Kemp at Albuquerque in which he went 5 for 7 with a double and two home runs and ran without discomfort in his left leg.

He also ran without discomfort during his first game back from the DL on Tuesday night against the Milwaukee Brewers, sprinting to first on a tapper back to the mound and also running out a double to the wall in the ninth inning.

"We have benchmarks and milestones in place,'' Falsone said of Kemp's previous rehab. "He achieved all those benchmarks and milestones, or he wouldn't have been out there playing. We will put him through the same repetition as before ... but we have to take a little longer to do it this time."

Asked the best-case scenario for Kemp's return, Falsone put it at four weeks, which means Kemp wouldn't return until late June. She also said Kemp could deal with hamstring issues for the rest of his career.

"There will always be scarring," Falsone said. "The only tissue we have that is as strong after healing as it was before is bone. Any other tissue heals with scarring, and scar tissue is inherently weaker than original tissue. So there is a little bit of susceptibility."

Castellanos, 25, was hitting .379 with 10 doubles, four triples, five homers and 14 RBIs with a .476 on-base percentage in the hitter-friendly Pacific Coast League. He played seven different positions there, but he also missed a month with a left hamstring injury.

Castellanos was expected to arrive around game time Thursday night against the Brewers. Dodgers manager Don Mattingly said Castellanos will be used primarily in the outfield and that he likely will be in the starting lineup on Friday night at the Colorado Rockies because left-hander Josh Outman is scheduled to pitch for the Rockies.