"For right now to start the season this is what's best for our team," manager John Farrell said of the decision Thursday. Farrell said salary is not his concern when determining the best lineup for the Red Sox.
Shaw's 2016 salary is the league minimum of $520,000.
Sandoval said the decision from Farrell was difficult. But did say Farrell's call was "the right decision to help the team win."
Shaw, 25, has better range, Farrell repeated Thursday after meeting with both players.
Sandoval, an eight-year veteran, signed as a big-ticket free agent before last season. He'll be on the bench for Opening Day with outfielder Rusney Castillo, who was signed in 2014 out of Cuba and given a $72.5 million contract.
Shaw played in 47 of the final 48 games for the Red Sox under interim manager Torey Lovullo and got off to a brilliant start at the plate this spring.
The quality of his at-bats and avoiding strikeouts are credits to Shaw, whom teammates say carries himself like a 10-year veteran. He broke in last August, smacking a pair of home runs in a game twice in a two-week span that month.
With his strong throwing arm, defense has always been a plus for Shaw.