D-backs outfielder Kole Calhoun had surgery to remove a split hamstring tendon in his left leg and could be out for six to eight weeks, depending on how the healing process goes.

Calhoun sustained a strained hamstring while attempting to steal third base in the sixth inning Tuesday night against the Padres. Calhoun missed the first seven games of the season after having surgery on his right knee earlier in Spring Training.

"My understanding is, there are other tendons that will bear the load in that area," D-backs GM Mike Hazen said. "It¡¯s a procedure that had been done in other [sports] -- the NFL specifically -- it has been done before."

Calhoun's is the latest in a string of injuries that have bitten the D-backs hard in the season's first month.

Fellow outfielders Ketel Marte (strained right hamstring) and Tim Locastro (dislocated pinkie) are also on the injured list, as is closer Joakim Soria (strained left calf) and setup man Tyler Clippard (strained left calf). Starting pitcher Taylor Widener (right groin strain) was placed on the injured list prior to Wednesday's game against the Padres and first baseman Christian Walker remains there after suffering a strained right oblique.

Despite all that, the D-backs went into Friday night's game against the Rockies with a 13-12 record.

"I am very proud of the fact that these guys play as hard as they do every night," Hazen said. "I¡¯m not surprised by that, given that we¡¯ve watched that for five straight years. But I think teams go through challenges and those challenges come in different forms. Our challenge right now is to keep ourselves where we need to keep ourselves until guys get back. The good news is, we are expecting everybody to come back and hopefully by the end of this weekend into next week we¡¯re going to continue to see those guys come back. But it¡¯s been a lot."

Locastro and Soria seem the closest to returning and Walker might not be far behind.

Marte has started to do some running in addition to hitting and throwing, but the team is being very cautious with him and he figures to be behind the other players in returning. A recent MRI showed that there had been healing, but there is still more to go.

"I don¡¯t have a firm timeframe on it yet," Hazen said. "It will still be a little bit of time. We¡¯re not in that zone where I can tell you where this is all going to fall. He is out doing activity, but we want to make sure we take care of this and do it right and put him in a position of going full bore for the rest of the season."