"Feels better -- feels better than it did," Jennings said. "Every day. It's gotten better the last couple of days."
Jennings, who is hitting .270 with three home runs and 11 RBIs, left Sunday's game in the second inning, shortly after sliding into home; he then ran slowly to first base. Jennings now believes that the slide caused the injury.
"I didn't feel it right away," Jennings said. "I went back to the dugout and sat down a minute. I got up and I just slid in home, so I figured I was just a little sore. Then I went out to the outfield, and it didn't feel good.
"[I felt sore] before [running to first base], and I just figured something was up. I just didn't want to mess it up more than what I thought it was already. I didn't want to do too much on it to make it worse."
When asked if he would be available on Tuesday night against the Yankees, Jennings said: "I don't know, but probably not."
Jennings also told reporters that he has injured his right knee in the past.
"Yeah, I hurt my meniscus in my right knee a few years ago, but nothing close to the feeling of this," Jennings said. "That was way worse."
Jennings sounded adamant that his injury will not be a long-term concern.
"I don't think I'll have to go on the DL," Jennings said. "I don't plan on going on the DL. I don't think it's that bad."
Rays manager Joe Maddon held out hope that Jennings might be available for pinch-hitting duty on Tuesday night. Jennings was asked when he might play again.
"Hopefully Wednesday," Jennings said. "I really don't know."