"J.D. has advised me that his decision is about assuring that he plays for a competitive team and wanting to continue to play in a place where he knows that he can be highly productive," Boras said in a statement.
No adjustments were made to the agreement initially signed in February 2018, Chris Cotillo of MassLive.com reports. Martinez, who will make $23.75 million next year, still holds additional opt-out clauses after the 2020 and 2021 seasons.
He also has a limited no-trade clause allowing him to block deals to three teams of his choice. The three teams aren't known, though he'll apparently have a chance to change the list (if he chooses) this month, according to Cotillo.
Had he opted out, the 32-year-old would have become one of the top bats on the market after two spectacular seasons in Boston. But the extent of Martinez's market as a free agent wasn't quite clear. Despite the lethal bat, his outfield defense - never a strong point in his game - has declined considerably, leaving him potentially limited to American League teams as a future full-time designated hitter.
Martinez won the Hank Aaron Award as the AL's top offensive player in his first season with the Red Sox, and also earned a pair of Silver Slugger awards (one each at outfield and DH) and a fourth-place MVP finish in 2018. This year, he got into 146 games and slashed .304/.383/.557 with 33 doubles, 105 RBIs, and a team-high 36 homers.
Martinez's decision to remain in Boston could have a massive effect on the Red Sox offseason. The club is looking to slash payroll and get under the luxury tax, and rumblings about possibly trading one of Martinez or superstar outfielder Mookie Betts - or perhaps both - in order to accomplish this have grown louder in the offseason's early days.