"Just so-so," McClendon said. "It wasn't great. The running part was a tick below average. It was his first time out with cleats on, running the bases. So you expect it to be a little stiff. He actually swung the bat OK."
But Jackson will need to improve some before being cleared for a Minor League rehab stint, which would precede his return to the Major League roster.
"The cutting action and stop and go, if he had to go right now he wouldn't be able to do that," McClendon said. "It's going to be more controlled right now, before we send him out on a rehab session."
Jackson will be eligible to come off the DL Tuesday, but McClendon figures he'll likely need a few more days before possibly joining Triple-A Tacoma by the weekend.
"That's our hope," he said. "We'll see how he progresses over the next few days."
• Logan Kensing, a right-handed reliever who went 6-3 with a 3.58 ERA in 49 appearances for Tacoma last season, signed a Minor League deal with the Mariners on Wednesday and was assigned to extended spring training in Arizona. Kensing, 32, has seven seasons of Major League experience, including six years with the Marlins, and is 8-9 with a 5.79 ERA in 135 big league games.
• Nelson Cruz entered play Wednesday leading the American League in home runs (15) and batting average (.349) and one behind Oakland's Stephen Vogt for the most RBIs with 29. After Cruz led the AL in home runs in April with 10, teammate Logan Morrison had the most homers in the league in the first 12 days of May with five.
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.