"It's all right, it's better," Jennings said. "It's something I'm trying to figure out. [I'll] start doing some stuff to loosen up."
Jennings said the tightness began "a day or two" before Thursday's off-day.
"I didn't think anything of it," he said. "Just figured it's a little tight.
"I feel it swinging a little bit. It's just one of those things that, I don't know, man, swinging ... I felt it tighten up running a little bit. I've been doing some things to get it right, to get it loose."
The Rays fly to Baltimore on Monday to begin a three-game series against the Orioles before heading to New York to play the Yankees next weekend. Jennings plans to work out at Tropicana Field prior to the team's departure. Included in his workout will be hitting and "rotation stuff," in his words.
Jennings has not had an MRI.
"It's all right," he said. "It's nothing serious. So I plan on playing Tuesday."