Chris Young on 15-day DL

NEW YORK -- There are more questions than answers surrounding Chris Young's shoulder injury.

The New York Mets placed Young on the disabled list Sunday afternoon because of tightness in the back of his right shoulder.

But there's a strong possibility the team will be without Young for longer than a 15-day disabled list stint.

An MRI on Sunday revealed swelling in the back of the right-handed starter's right shoulder. There is a concern that Young aggravated the same shoulder injury that limited him to just four appearances in 2010.

Mets general manager Sandy Alderson said there is "swelling in the back of his shoulder in the area of an old injury ... We're not sure the extent of this injury."

Alderson added that he would be "surprised" if Young made it back to the mound before May 17, when the right-hander is eligible to come off of the disabled list. The Mets expect to know more on Monday after a second physician examines the MRI.

Young has suffered through several shoulder injuries in recent seasons. He made just four appearances with the San Diego Padres last season because of lingering shoulder ailments related to a surgery to repair tendinitis he underwent in 2009.

Alderson could not rule out the possibility that Young had aggravated the injury or suffered a new tear in his shoulder muscle.

"There isn't really a definitive diagnosis at this point," Alderson said.

The GM hopes that the second opinion will determine whether Young (1-0, 1.88) has suffered a new injury, aggravated an old one or had an acute reaction to a chronic condition.

The team has called left-hander Pat Misch up from Triple-A Buffalo to replace Young.

Young was not able to make his start on Saturday because he felt tightness in the shoulder while long-tossing in the outfield before the game.

Young, who signed with the Mets as a free agent in the offseason, received two anti-inflammatory injections during the week.

Dillon Gee, who made an emergency start in place of Young on Saturday, temporarily could step into Young's spot in the rotation -- though Young's next turn in the rotation is Thursday, which is an off day between road series in Colorado and Houston.

Young was placed on the disabled list on April 16 with bicep tendinitis at the spot where the bicep meets the shoulder. He was activated on April 26 and made a start at Washington that day and at Philadelphia five days later. He received a no-decision after both outings.

Alderson said that the Mets would use greater sensitivity in treating Young's most recent injury.

"This could be a little bit more significant than anything we've seen over the first few weeks so we're just going to have to wait," Alderson said.

Young downplayed the severity of the injury on Saturday night.

"Last year I could barely even pick up a ball," he said. "... This, I can go through the motion. It's just grabbing as I try to increase the intensity."

Alderson said on Sunday that Young was disappointed by the injury and the fact that he wouldn't be able to contribute to the Mets (15-19), who have won three of four heading into a seven-day, six-game road trip that starts Monday in Colorado.

"He feels like he's letting us down and I tried to reassure him that, look, we all understood the risks associated with his signing and his pitching," Alderson said. "So this isn't entirely unexpected."

Alderson signed Young to a one-year contract worth approximately $1.1 million that could grow to as high as $4.5 million if Young reaches certain incentives.

Alderson said he understood Young's injury history before signing him. He didn't second-guess the signing in light of the injury and held out hope that Young could be a consistent contributor for Alderson in his first year as general manager.

"We're only in the first month and a half of the season. ... I'm still hopeful he's going to continue to be productive but on a more frequent, consistent basis for us. We're going to have to wait and see," the GM said.

The team also moved Johan Santana from the 15-day disabled list to the 60-day disabled list. That's simply a clerical maneuver that avoids Santana counting against the 40-man roster. He is still expected to get on a mound this week and return in July.

Misch, 29, spent a two-day stint with the Mets earlier this season. The lefty went 0-4 with a 3.82 ERA in 12 games (six starts) for the Mets last year. He is expected to contribute as a long reliever out of the bullpen.

Alderson expressed concern with the pitching staff's depth in light of Young's injury. He said the team may have to search for some serviceable pitching outside of the organization if another starter or reliever is lost to injury.

Ian Begley is a regular contributor to ESPNNewYork.com.