Montero, 22, said he was out of sorts on Tuesday, but was cleared to play after going through a full workout on Thursday after the Mariners got to Oakland prior to re-starting the regular season on Friday.
"Yeah, everything is good," Montero said. "It took a couple days. The next day, I was feeling dizzy and [had] a lot of headaches. But after that, I was good. It was a big hit."
Manager Eric Wedge waited to see Thursday's workout before penciling Montero back into the lineup. The youngster is expected to be a big part of Seattle's offensive attack this year, after being obtained in the Michael Pineda trade with the Yankees in January.
Montero hit .326 with two home runs and a team-leading 13 RBIs in 13 Cactus League games. He was 1-for-7 in the two opening games against the A's in Tokyo, while batting fifth.
"He had a good work day [on Thursday]," Wedge said. "He caught a long bullpen, took batting practice, ran around a little bit. So he's good to go."
Montero said he'd never been hit in the head before Escalona's pitch glanced off the side of his batting helmet in the Cactus League encounter.
"I was a little surprised. But there's always going to be a first time," Montero said. "I'm really happy to be back now. I cannot wait to be out there to help the team."