"Not being able to be out there battling with them is tough to swallow," Erlin said. "But hopefully, just finish the season strong. There's still four months left. Hopefully that's how it goes, and I can still make a bunch of starts."
The Padres recalled right-handed reliever Leonel Campos from Triple-A El Paso, but it remains unclear who will start in Erlin's place on Saturday against St. Louis.
Manager Andy Green ruled out Brad Hand, but said fellow reliever Carlos Villanueva could be an option. He also left open the possibility of adding a Minor League arm.
An intriguing option is right-hander Brandon Morrow, who has been recovering from shoulder surgery last August. He is slated to start Friday for Double-A San Antonio, but Green left open the possibility for Morrow to return to the big league club. Morrow was arguably the Padres best pitcher last April, before being sidelined in early May.
"Right now we'll play it a little bit close to the vest until we feel good about settling on a name," Green said. "... I don't know that it's too soon [for Morrow]. I would guess if you asked him, he wants the ball now, and he wants to be on the mound at Petco."
In 2014, Erlin missed nearly four months with an elbow injury. He said the current injury is the same part of the arm, but a different -- and potentially more benevolent -- diagnosis.
Erlin had pitched in three games this season, two of them starts. He was very sharp in his first two outings, allowing just one earned run over 9 2/3 innings. But the injury flared up on Sunday, and he was roughed up to the tune of six earned runs and three homers against Arizona.
"That was one of the factors with the decision-making," Erlin said of his struggles Sunday. "It was uncomfortable, a little tougher to accelerate and finish the pitch."
The injury news comes a day after the Padres announced that Tyson Ross' recovery from a right-shoulder injury had stalled, and two days after second baseman Cory Spangenberg strained his left quad while running to first base.
Ross, Spangenberg and Erlin join third baseman Yangervis Solarte (right hamstring strain), left-hander Matt Thornton (left Achilles tendinitis) and right-hander Jon Edwards (right elbow stiffness) on the 15-day DL.
"They're all competitors, they want to be on the field," Green said. "We've had a rash of injuries right here in the recent couple weeks to start the season.
"We get through Spring Training everything's perfectly clean, everybody's feeling great. Then the first couple weeks of the season start, and things aren't great. But every team's going to go through it."
Campos has appeared in five games for El Paso this season, allowing four runs on four hits while striking out 12 over 7 1/3 innings. He got a phone call from Triple-A manager Rod Barajas at 1 a.m. Thursday, telling him to pack his suitcases for his third stint in the big leagues. (Campos has allowed five earned runs in eight career innings.)
"This is my third call," Campos said. "It's not like the first time where you're all on edge and didn't really know what was going to happen. So, of course I'm happy to be back. This is the best baseball in the world in the big leagues."