Severino, who has been on the injured list with right rotator cuff inflammation and a lat strain, last pitched in the majors in Game 3 of the 2018 American League Division Series, when he gave up six runs in three innings of a 16-1 loss to the Boston Red Sox. He was 19-8 with a 3.39 ERA in the regular season.
"No question we're excited to get him back," Boone said. "I feel like he's been in a pretty good place physically now for a couple of months and building really good momentum. I feel like his progression has gone really smooth."
Boone added: "He could be a game-changer guy for us, there's no question."
Severino, who made his final rehab start for Double-A Trenton on Wednesday night, will rejoin the Yankees in Toronto on Friday. The team faces the Los Angeles Angels on Tuesday.
Boone hopes Severino can make three starts in the regular season.
"Not far off at all," Boone said of Severino's rehab outing. "Now it's just a matter of really just getting real sharp. But you can tell he feels good, the stuff is there. Now it's getting sharp with it and getting that consistency."
Severino threw 64 pitches over 3⅔ innings, striking out four with zero walks while giving up five hits and four runs (one earned).
"I feel pretty good," Severino told reporters after the game. "Today, I was looking forward just to seeing my arm. I was letting the ball go better than the first one. I was working on my secondary pitches. My changeup was down in the zone. I left a couple up, but I think that everything went well."