SAN DIEGO -- Just two weeks ago, the Padres' starting rotation appeared firm with Edinson Volquez, Cory Luebke, Dustin Moseley, Clayton Richard and Tim Stauffer.

Two disabled-list trips later, the rotation looks nothing like it did when the team broke camp in Arizona, not with Moseley out for an indefinite period after an MRI exam of his right shoulder revealed "extensive damage," according to manager Bud Black.

The Padres are hoping that Moseley won't need surgery, though he indicated after Tuesday's 4-2 loss to the D-backs that the MRI he had Monday showed "changes to the labrum."

"We'll give it some time to calm down," Moseley said. "Yesterday I was down in the dumps but today I'm doing better. We've give it a few days to calm down and see how it feels. We'll see if there's a possibility we can strengthen it and go from there."

Moseley went on the DL on Sunday, the day after he allowed five runs in five innings during a no-decision against Dodgers.

"He's going to be shut down for a period of time that will take him past 15 days," Black said. "I know it's frustrating. I'm bummed for him."

The Padres will use right-hander Anthony Bass on Thursday against the D-backs unless he is needed in long relief in either of the first two games of this series.

The Padres will also need a starting pitcher for Saturday against the Dodgers, the spot that would have otherwise been filled by Stauffer. Stauffer landed on the DL on April 4 with a strain of the right elbow.

"The rotation will look a lot different than it was supposed to 10 days ago," Black said. "... But we feel as though we have some depth."

Right-hander Joe Wieland, one of the Padres' top prospects, will join the team in Los Angeles for that start Saturday. Wieland struck out four over two scoreless innings for Triple-A Tucson on Tuesday before being informed by manager Terry Kennedy that he would be making his Major League debut Saturday with the Padres.

Kotsay to start rehab stint on Wednesday

SAN DIEGO -- Padres outfielder Mark Kotsay, on the disabled list since April 1 with a strained right calf, will start a Minor League rehabilitation assignment on Wednesday with Class A Lake Elsinore.

Kotsay, who suffered the strain in a Cactus League game in Arizona on March 31, will be eligible to return on April 16, the day that the Padres open a three-game series on the road against the Rockies.

"We'll evaluate him each day as he goes, but he's been feeling fine," Padres manager Bud Black said.

Kotsay ran in the outfield under the watch of Black and the training staff prior to Sunday's game with the Dodgers at Petco Park and tested his calf again before Monday's game against the D-backs.

"I'm going to run today and do my whole routine," Kotsay said as he raced off for his pregame work.