WEST PALM BEACH, Fla. -- Jon Lester is slated to make his Spring Training debut Thursday against the Mets in Port St. Lucie. The matinee start will be Lester’s first appearance as a member of the Nationals since signing a one-year deal in January.

“He says he feels real good,” manager Dave Martinez said Tuesday.

• Watch Lester's Nationals debut on MLB.TV

Lester, 37, underwent a parathyroidectomy (removal of a parathyroid gland) earlier this month to alleviate hyperparathyroidism. He initially chalked up feeling lethargic to getting older, but after doing research and speaking with an endocrinologist, he decided to go through the hour-long procedure in New York.

The southpaw returned to Florida last week, and he has been working his way back through live BPs and strength and flexibility training. He reached 40 pitches in a recent sim game.

“We definitely want to get him two innings,” Martinez said. “I figure: stretch him to get him into that third inning. We’ll see if we can do that.”

Lester is prepping for his 16th Major League season. Last year, he went 3-3 with a 5.16 ERA for the Cubs.

With Lester entering the rotation, Joe Ross’ next start will be moved to Friday night against the Astros.

Also on Thursday ...
The Nationals will keep their eyes on another pitcher Thursday, as Tanner Rainey is scheduled to throw a sim game. The right-handed reliever has been sidelined by collarbone soreness and has yet to appear in a spring game.

Rainey’s pitch count has ranged between 20-25 pitches to this point. He has built up to three outs, and Martinez would like to see if he can get to four on Thursday.

“If that goes well,” Martinez said, “hopefully we’ll get him in the game a few days after that.”

Once cleared to pitch, Rainey is poised to be a key member of the Nats’ late-inning bullpen. He posted a 2.66 ERA and 0.74 WHIP in a breakout 2020 season.

Return of a familiar scene
Following a season of the universal designated hitter rule, the Nationals got a look at a pitcher at the plate when Patrick Corbin took an at-bat in the third inning against Marlins starter Trevor Rogers on Tuesday. He struck out in his lone plate appearance of the game.

“First time in a long time, it felt like," Corbin said. "But I always enjoy doing it. It’s fun when you can go up there and put a good at-bat together. ... A little strange walking over there, putting your helmet on and getting your batting gloves again, getting used to that routine.”

On the mound, Corbin threw 68 pitches (37 strikes) over 3 2/3 innings. He allowed four runs, four hits (two homers), four walks and fanned two.