"He's doing better," manager Lloyd McClendon said. "He's going to run the bases a little today and do some hitting. There's a chance he could be going out on a rehab soon."
Could he be ready to return by May 19, the first day he's eligible to come off the DL?
"We'll see how he progresses," McClendon said.
Jackson said he's uncertain on a timeframe, but has been feeling better.
"I did a little running on Sunday and everything went good for the first time," he said. "I didn't have any pain, so that's always a good thing. I'll do the same thing today and see how it reacts after another day of running.
"We haven't really talked about the plan. I guess we'll see over the next couple days when I start doing a little more out in the field."
Jackson twisted his ankle when stepping on the corner of the first-base bag trying to leg out an infield single on May 3 in Houston. He hit .242 with 11 runs, five stolen bases, two home runs and four RBIs in 25 games before his injury.
• The Mariners are flip-flopping Taijuan Walker and Roenis Elias in their rotation, with Walker moving up to face the Padres on Wednesday night and Elias facing the Red Sox in Thursday's series opener.
"It really didn't have a lot to do with them," McClendon said. "It's more so trying to line up our lefties against Boston and make sure we could get them all facing Boston. And it doesn't hurt to have a righty against [the Padres] either."
Southpaws J.A. Happ and James Paxton will face the Red Sox on Friday and Sunday, sandwiched around Felix Hernandez's Saturday outing. McClendon said he hasn't decided yet if he'll use next Monday's off-day to skip anyone or make any further rotation adjustments. That will be Seattle's last day off before a 20-game stretch.
Greg Johns is a reporter for MLB.com. Follow him on Twitter @GregJohnsMLB, read his Mariners Musings blog, and listen to his podcast. This story was not subject to the approval of Major League Baseball or its clubs.