Sandoval will report to camp on Saturday, three days before position players are due in.
"He went through some extensive work this past offseason, trying to get back to putting himself in a better position," said Red Sox manager John Farrell. "He's revamped his right-handed swing. For those who are familiar with what that looked like last year, I think you'll see a difference when he gets here."
Sandoval hit .197 with no homers and 11 RBIs against lefties last season. In his career, he is a .259 hitter against southpaws.
• Farrell is enthused by the health of catcher Christian Vazquez, but feels it's too soon to determine if he'll be ready to start the season in the Major Leagues. Vazquez underwent Tommy John surgery last March.
"We'll take all of Spring Training to determine that. The expectation on Feb. 18 of where a catcher would be coming back from Tommy John ... I would say he's ahead of it," said Farrell. "He's thrown to the bases multiple times now with good aggressiveness and intensity. He's had no residual effect the next day. He's doing a great job. If you look at the body and shape he's come in with, he's handled everything he's been asked to do from a rehab and conditioning standpoint.
"He's put himself a great position physically. Once we get into games, we'll get a better understanding how many games a week he will be capable of."
Blake Swihart is the frontrunner for the team's starting catcher spot, and veteran Ryan Hanigan is still on the roster as a backup.
• Veteran non-roster invitee Carlos Marmol, who was acquired earlier this week, was in camp on Thursday. What leads the Red Sox to believe Marmol might be able to regain the form that once made him a solid reliever?
"We're looking at Carlos as a little bit of a bounceback candidate," said Farrell. "Over the past couple of years, we've gone back in time -- and this is where Brian Bannister has come into play quite a bit on the examination of this. I don't want to say it's a project, but he's a guy that's been a frontline closer over the past couple of years.
"His arm slot has changed dramatically, as has the action to his sinker and his slider. Prior to signing, there was a pretty detailed plan of what we want to do with readjusting the arm slot to get him back to where he was when he was the closer with the Cubs. He's eager to do it. He was in agreement that adjustments are needed."
Ian Browne is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.