FORT MYERS, Fla. — Red Sox Nation can officially begin worrying about David Ortiz.

The big designated hitter, who represents perhaps the most important piece of the Boston lineup, still feels pain in his injured right Achilles, seven months after suffering the ailment. He didn’t sprint all winter and spent the early portions of spring training trying to run the bases, with varying degrees of success.

An MRI on Saturday revealed that Ortiz is suffering from inflammation in both heels, and as a result, he was shut down for five to seven days.

Manager John Farrell indicated the setback probably means Ortiz will not be ready by opening day.

“We got the MRI results back,” Farrell told reporters. “It does reveal some inflammation in the bony area of the heel. He’s dealing with that. That’s where the discomfort is being felt. As a result, we’re going to shut him down for a few days here to let that quiet down completely before we start to initiate any kind of baseball activities.”

Ortiz has mainly been having pain in both heels but specifically the right one, which he injured in July.

“We feel like progress is being in made,” Farrell said. “There’s no doubt about that. But he’s dealing with an issue that we’ve got to give it time to clear up.”

The 37-year-old Ortiz batted .318 with 23 homers last year before an Achilles injury first occurred in July.

“Like I said, it is what it is and things happen for a reason, right? The one thing that we’re really working on is that when I’m back, I’m back,” Ortiz said on the Red Sox website Monday. “It’s not just coming back for a couple of weeks and then going back and doing the same thing. They’re trying to fix the whole thing. That way when I get back in the lineup, it’s going to be there, and be there for the season.”

Preseason workouts have been difficult for Ortiz.

“I knew it was something, it was not normal. I was getting pain four or five hours after I was finished with my workout and I knew something wasn’t right,” Ortiz said on the Red Sox website. “We had that communication between me and the doctors, the trainers. They agreed with getting an MRI just so we could see what was going on. It’s not anything crazy, thank God, but it’s going to take a couple of weeks to get fixed.”

In Monday’s game against the Marlins in Jupiter, Fla., the Red Sox took a 7-1 lead into the bottom of the seventh, but the Boston bullpen collapsed and gave up five runs in the seventh and two in the ninth to suffer an 8-7 loss.

In the seventh, Boston’s Rubby De La Rosa gave up five runs on two hits and four walks in two-thirds of an inning. In the ninth, Kevin Kouzmanoff belted a two-out, two-run home run off Boston’s Chris Carpenter.

Jackie Bradley Jr. paced Boston with a solo home run and RBI double. Mike Carp also cranked a solo homer and Will Middlebrooks added a two-run shot in the seventh.

Red Sox lefty Jon Lester turned in a strong outing as he gave up only one run in five innings while striking out four. He retired the last 11 batters he faced.

On Tuesday at 1:35 p.m., Clay Buchholz gets the start for the Red Sox against the Blue Jays in Fort Myers, Fla.