The Angels, getting ready to play the Twins in the finale of a dismal road trip that has produced one win in five games, had no immediate comment on the prospect of reacquiring O'Day.
O'Day, 26, appeared in 30 games for the Angels last season, with a 4.57 ERA in 43 1/3 innings. He yielded 49 hits and 14 walks while striking out 29 hitters.
O'Day made the Opening Day roster in 2008 as a long shot, making the jump from Double-A Arkansas with a brilliant spring. He made 14 appearances in April with a 2.04 ERA.
The Angels added two arms to their bullpen on Saturday. Right-hander Rich Thompson got five outs in a 9-2 loss to the Twins, while southpaw Daniel Davidson did not make an appearance. When he does, it will be his Major League debut.
The Angels' bullpen has a collective ERA of 8.55 across 33 2/3 innings, compared to a 2.74 ERA by the starters, second-best in the American League.
Manager Mike Scioscia said the club will make a decision in the next few days how to fill rotation spots on Thursday at Angel Stadium against the Tigers and on Saturday against the Mariners.
Darren Oliver made it through four innings on Saturday night, allowing just one run against the Twins, and remains a possibility for Thursday night. But Scioscia clearly prefers to have the veteran available for relief.
"More options are evolving," Scioscia said on Sunday morning. "There are some things we're going to look at, whether to keep Darren Oliver in the rotation or bullpen."
Compounding the rotation problems, Dustin Moseley went to the 15-day disabled list on Saturday with right elbow stiffness and will not be available until May 3.
This leaves Scioscia with three starters -- Joe Saunders, Jered Weaver and Shane Loux.
John Lackey (right forearm strain) and Ervin Santana (right elbow sprain) had strong bullpen sessions on Saturday and rebounded well the following day, Scioscia said, but they'll need several tuneups before being ready to rejoin the rotation. Both are shooting for early May.
Kelvim Escobar (July right shoulder surgery) also has resumed playing catch and hopes to be back in May as well.