Scioscia, though, was impressed by Palmer's performance during Spring Training, during which he posted a 4.91 ERA in eight appearances.
"Matt's a guy with some Major League experience, and over his last couple outings, his stuff has picked up," Scioscia said. "He's a guy that can give us a chance to win us a ballgame. We feel he's one of our best short-term options."
Palmer will make the start in place of Darren Oliver, who was moved back to the bullpen after tossing four innings on Saturday against the Twins.
Scioscia said Oliver is feeling stiffness in his left arm but would not have started Thursday even if he was completely healthy.
"I think when Darren's in the bullpen, he can pitch four or five games in a week and do a great job, as opposed to pitching in just one game," Scioscia said. "If you look at the continuity of our bullpen, Darren will go a long way to helping us with those things."
The Angels will have to clear a spot on the 25-man roster for Palmer, but the move will not be announced until after Wednesday's game.
The club will also have to open a spot on the 40-man roster, but it appears as though Kelvim Escobar will be moved to the 60-day disabled list, retroactive to April 3, to make room for Palmer.
Escobar suffered a setback in his return from right shoulder surgery and said he won't be ready to come back until June instead of May, as was thought to be the case.
"If I come back as a starter, it's going to take a while," said Escobar, who is only playing catch at this point. "I have to build up to 100 pitches, so that will take four or five games, which is at least a month."
Escobar will extend to throwing from 170 feet before throwing bullpen sessions this weekend. But he said he'll be cautious this time because he said he rushed himself too much in Spring Training.
"I think I did too much, too soon," Escobar said. "I was anxious and happy about how I felt. When I saw [John] Lackey and [Ervin] Santana go down, I think I was trying come back quicker than I needed."
The Angels also need to name a starter for Saturday's game against the Mariners, but Scioscia said an announcement won't be made until Friday.
Scioscia, though, has mentioned Triple-A righty Anthony Ortega as a candidate, as well as Double-A righties Sean O'Sullivan and Jordan Walden and Class A lefty Trevor Reckling.
Of that group, only Ortega is on the 40-man roster.