Dodgers' Matt Kemp out at least four weeks with hamstring injury Reality called the Dodgers Thursday, and it might as well have been a siren beckoning them into the rocky shore. The results of the MRI on Matt Kemp's hamstring showed he not only re-injured the original strain Wednesday but suffered a second one. Dodgers trainer Sue Falsone said he's expected to be out a minimum of four weeks. That's a best-case scenario, and even Falsone was uncertain if he would be able to return to a major league game by then. Kemp was placed back on the 15-day disabled list he had just come off of from his initial hamstring injury Tuesday. The Dodgers called up outfielder/infielder Alex Castellanos to fill his spot on the roster, but obviously not his place on the team. Castellanos was scheduled to join the team prior to game time. Manager Don Mattingly tried his best to put a brave face on. "It should be a good time," Mattingly said. We'll find out what kind of club we are. We were able to find out for a couple of weeks when Matt was out and guys stepped up. And we're going to have to do it again. We'll learn more about our team. Are we going to bend but not break? We'll see what happens. Falsone said both strains are rated as grade one, the lowest level, and the second was slightly higher in his left leg. "Obviously having two different strains in one muscle, it's going to be a little longer from a rehab standpoint," she said. Kemp returned from his MRI just before the Dodgers took the field Thursday for their pregame workout and immediately went into the trainer's room. The re-injury, and new injury, came Wednesday as he scored from first on a double by Andre Ethier in the first inning. Kemp started to slow down as he approached third, but when center fielder Carlos Gomez bobbled the drive he accelerated again to score, possibly when the leg gave out. "I don't think we can say the first strain caused the second strain," Falsone said. It takes the body time to heal and he reached all those milestones before, so now he has this new strain. Physics happen. Kemp will have missed almost two months of games by the time he returns, and then he will have to get his swing back. Kemp was the National League Player of the Month in April (.417, 12 homers, 25 RBI, .490 and .893 on-base and slugging percentages). And then, of course, there is always the danger he injures it again. Falsone said only bone heals as strong as it was before injury. "Any other tissue in the body heals with scar," she said. Scar is always inherently deeper than original tissue. So anytime you have any type of issue with scar tissue, you always have a little bit of susceptibility to weakness in that area. The Dodgers went 9-5 while Kemp was on the DL the first time. Outfielder Juan Rivera, currently on a rehab assignment with his own hamstring injury, is expected to rejoin the team this weekend. Alex Castellanos called up to replace injured Matt Kemp