Shields has been sidelined by a right forearm strain, which surfaced as he was coming back from shoulder soreness. He is being treated, and says he feels "much better," but he doesn't know if he'll get enough work in by Opening Day to assume his spot on the pitching staff.
"I want to be there," Shields said. "It might be a long shot, but I'm still shooting for it. I have come to the realization that it's a possibility that [starting the season on the disabled list] can happen.
"I'm not trying to throw through the pain. It's not anything I want to mess around with. I wouldn't want to miss a season by trying to rush it."
If Shields opens the season on the disabled list, getting his arm in shape in extended Spring Training in Arizona, fellow setup man Justin Speier would inherit the Angels' eighth-inning role. Speier has retired all 15 hitters he's faced in Cactus League play.
What makes his situation difficult to accept, Shields said, is his history of reliability for his team. Shields has led the American League in holds the past two seasons, and has pitched more innings over the past four seasons than any reliever in the Majors. Yet his total innings have dropped in each of the past three seasons, from 105 1/3 in 2004 to 91 2/3 in '05, 87 2/3 in '06 and 77 in '07.
"This is the first time it's come up, the possibility of missing time," he said. "It never happened in college, the Minor Leagues, anywhere."
Judging by his treatments, Shields said the improvement in his forearm is significant. He hasn't thrown since Wednesday, when the pain surfaced while he was pitching a two-inning stint in a Triple-A Spring Training game.
"It's getting a lot better," he said. "With the pressure points five days ago, I was in pain when they were barely touching [the arm]. Now they're digging in, and it's fine."
Manager Mike Scioscia indicated that it's doubtful Shields will be ready, creating an opening in the bullpen for the likes of Darren O'Day, Rich Thompson, Jason Bulger or Alex Serrano.
"We're not totally eliminating Opening Day from where Scot is," Scioscia said. "He's feeling much better, and we're encouraged. He's going to be picking up a ball, getting on a mound to fine-tune some things. But we're not trying to cram anything to get him ready for Opening Day."
Lyle Spencer is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.