Mattingly said the Dodgers intend to wait at least 24 hours before the MRI because the dye used to enhance the image could potentially increase swelling in his shoulder.
"He felt a whole lot better this morning," Mattingly said. "I think the good thing from our standpoint was [when] he had a similar injury this winter in the Dominican [Republic], he was hitting within four days. He feels like this is less than that. That's all we have to go by. His movement is a lot better today than yesterday, and we'll probably even know more by the end of the day."
Yasiel Puig felt good enough to return from a contusion on his left thumb suffered Saturday to start in right field for the opener against the Cardinals in St. Louis.
"He's in there, so obviously he's feeling a lot better," Mattingly said.
Matt Kemp said Monday his sprained left ankle is progressing well. Currently on the 15-day disabled list, Kemp is still using a walking boot, but said he is feeling better each day.
"Ankle injuries take time. That's what it's doing, it's taking time and hopefully I'll be back soon," Kemp said. "I just go on how I feel. If I feel good, I do more. If I don't, I back off a little."
Chad Thornburg is an associate reporter for MLB.com.