Twins catcher Jason Castro has a concussion, Zack Granite recalled from Rochester

CHICAGO – Jason Castro's mild dizziness didn't worsen overnight, and he has reported no sensitivity to light or noise, common symptoms of concussions. The Twins have two other catchers on the roster, so there was no urgent personnel reason to rush into a transaction.

But the Twins, an organization that has learned firsthand about the hidden, lingering effects concussions can have on players, chose Thursday to sideline the catcher for at least a week anyway, a reflection of the increased caution MLB uses when dealing with head injuries.

"We knew we could wait until today and see how he feels," assistant General Manager Rob Antony said, one day after Castro reported feeling dizzy after a series of foul balls off his mask during Wednesday night's loss to the White Sox. "But last night, we just decided, let's get [Zack] Granite here."

Castro, placed on the seven-day concussion list, is the third Twins regular in the past week to be sidelined by injury, after Robbie Grossman's fractured left thumb and Miguel Sano's stress reaction in his left shin. That's not ideal, but it's better, the Twins decided, than risking Castro joining Justin Morneau and Joe Mauer as long-term victims of a blow to the head.

Castro told the Twins he has had a concussion once before, the result of a collision at the plate when he was a rookie in 2010. "You never know — every one of them is different," Antony said. "It's really hard to tell the severity. It could be minor, he could have a headache for a couple of days. You don't know."

He will be eligible to return Wednesday, but only after successfully completing a series of concussion tests to make sure, as best as possible, that there are no lingering effects.

Castro, who has started 86 of the Twins' 126 games, will remain with the team and watch Chris Gimenez and rookie Mitch Garver do the catching in the meantime, though the Twins offered to let him go home.

Castro won't be the only injured player in uniform in Toronto. Grossman, who figures to miss another two to three weeks, has been along, too, a reflection of his impact in the clubhouse, Molitor said.

"I like Robbie's presence," Molitor said.

Grossman said he's flattered, and he's trying to be as useful as possible as he waits for his thumb, fractured during a collision with Byron Buxton in the outfield, to heal. "I'm very appreciative. It's a great group of guys, and we have a bond and a connection that's about more than baseball," Grossman said. "Everyone really enjoys being around each other in this clubhouse."

The swelling has disappeared, so Grossman can shag fly balls during batting practice (and flip them back with his glove hand), do extra cardio work, and even run pass patterns, with strength coach Perry Castellano as quarterback, in the outfield.

And during the game, he's trying to help his teammates. Wednesday, when the Twins were in the field, he went to the clubhouse to watch video of Chicago's James Shields, who is using a more sidearm style this year.

• Adalberto Mejia "did very well" during his bullpen session Thursday, Molitor said, and will throw again Sunday as he recovers from a strained bicep.