BOSTON -- Tyler Thornburg will begin a rehab assignment tomorrow (Monday) at Triple-A Pawtucket.

The late-inning reliever is returning from surgery to treat thoracic outlet syndrome in his right shoulder last June. He missed the entire 2017 season.

"It's kind of spring training for him," Red Sox manager Alex Cora said. "It's a process. Obviously we'll want him to go back-to-back days. It's a longer process. But the fact that he's going to be pitching tomorrow, that's great. Great for him honestly. Going into spring training, everybody knew his situation. And for him to grind it out and put himself in this spot is awesome. And obviously for us, it's great. It's going to be a great day for him and the organization."

Thornburg posted a 2.15 ERA, 0.94 WHIP and 13 saves in 67 outings (67 innings) for the Brewers in 2016. He was one of the best setup men in baseball before undergoing surgery.

He reached 95 mph on the radar gun in extended spring training games.

Thornburg averaged 94.1 mph during 2016 with the Brewers, per Fangraphs.com.

"He's throwing the ball well," Cora said. "Velocity's up. The offspeed pitches are a work in progress. But I think challenging him at that level, it will be good for him. He has to pitch. It's not like staying in Florida and facing kids and just throwing your fastball and getting outs. I think facing higher-level hitters for him is going to be a challenge. And he's up to it."