Catcher Jason Castro was eligible to come off the disabled list Tuesday but will now miss at least another month after undergoing surgery on his right knee.
Castro has been sidelined since May 5 and received a cortisone injection in order to avoid surgery. But it didn't work as hoped so the veteran backstop sought a second opinion from De. Robert Laprade, who recommended surgery.
"It's disappointing," Molitor said. "Hopefully we'll get a better feel on length of rehab once the procedure is completed."
That leaves Mitch Garver as Minnesota's primary catcher when the team resumes its home stand Tuesday against the Cardinals at Target Field, where Garver is batting .316 this season.
"With him and Bobby (Wilson), we're trying to match up the best way we can," Molitor said. "They're both going to get a chance to get a fair amount of time back there. For Mitch, he's starting to get more comfortable in the batter's box ... just a good opportunity."
The Twins were also hoping to get third baseman Miguel Sano back this week but he, too, will need a little time. Sano worked out before Minnesota's game Monday against Seattle and wasn't close to 100 percent.
"I'm hoping we can have a good week here and think about getting him into a game sometime sooner than later, somewhere," Molitor said. "Those hamstrings -- to practice and try to get ready to go into a game and then be able to sustain for nine innings multiple games consecutively, that's a challenge."
After dropping a pair of one-run decisions, the Twins turn to right-hander Jose Berrios to get the team back on track Tuesday.
Berrios, though, is battling through a rough patch. He has an 8.84 ERA through his last four outings and gave up five runs over 5 1/3 innings in his last outing.
He'll face Cardinals rookie Jack Flaherty, who returns to the big leagues for the first time since holding the Pirates to three runs over five innings on April 28.
Flaherty is 0-1 with 11 strikeouts over 10 innings in two starts for St Louis this season and 4-1 with a 2.27 ERA in five starts for Triple-A Memphis.
Flaherty struck out 13 in his last outing for the Redbirds. He's relied heavily on a sinker of late and as a result, has 19 groundouts compared to just eight fly balls with 12 hits allowed.
"Whatever it is about Jack's (sinker), it gets more swings and misses than anybody else," Cardinals manager Mike Matheny said. "He's got a nice idea when to use it in the zone. He gets chases with it. He just has this whole package that is pretty polished for as young as he is."
The Twins swept the Cardinals in a two-game interleague series last week in St. Louis. Minnesota pitchers allowed just one run in those contests while the Twins' offense scored a combined 13 runs.