FORT MYERS, Fla. — The Twins were already expecting to be without two of their top relievers to begin the season. Now, they’ll have to weather at least the beginning of the season without another bullpen arm who they figured would be throwing important innings.

Justin Topa, whom the Twins acquired earlier this year in the trade for Jorge Polanco, tweaked his left knee and is dealing with tendinitis, president of baseball operations Derek Falvey said.

Topa, who hasn’t pitched in a Grapefruit League game since March 15, will begin the season on the injured list, joining closer Jhoan Duran (oblique strain) and lefty Caleb Thielbar (hamstring strain). Falvey said the injury occurred when Topa went to back up home in a game and his foot got jammed up.

“We don’t want tendinitis to track through the year if we can knock it out ahead of time, so we’re going to knock it out now, give him some time down and ultimately build back up,” Falvey said. “Hopefully he’s not tracking foo far behind.”

The Twins plan to shut him down for a week to 10 days, a period that has already started, treat the issue and then start to build him back up.

Topa, 33, played a major role out of the Mariners’ bullpen last season, posting a 2.61 earned-run average across 69 innings while establishing himself as a set-up man.

Now, with Topa, Duran and Thielbar out, the Twins will have to turn to other options to fill out their bullpen. While they appeared to have one roster spot open to begin camp, they now have four. Twins manager Rocco Baldelli said that while they would like to have everything wrapped up while they are still in Fort Myers, they could end up making decisions once they get to Kansas City, where they will open their season. The Twins will depart Florida following the conclusion of their last Grapefruit League game on Tuesday.

“There’s still things to be discussed and at this moment in time, we’re talking mainly about our bullpen and just where we’re going to land there,” Baldelli said. “The goal is to get out of camp, at this point, with only that to talk about, and if that happens, that’d be pretty solid. But we’ve got to get through the next couple of days.

The Twins have a number of relievers in the mix for those spots, including Jorge Alcala, Josh Staumont, Kody Funderburk and Cole Sands, all of whom are on the 40-man roster. They also still have some non-roster options, with Daniel Duarte at the front of that group if the Twins choose to go in that direction, or they could also make an external addition.

“We are monitoring the opt-outs and guys who are around and available and having conversations with different people,” Falvey said. “More just as we continue to build up depth, we have guys in camp who we think can do some of this, certainly fill some of these roles. It never hurts when you’re down a few to keep an eye on how to add to that depth. We’d be doing that even if we weren’t dealing with some injuries.”