Boston Red Sox slugger J.D. Martinez has decided to not opt out of the final three years and $62.5 million remaining on his contract, according to ESPN's Jeff Passan. Instead, Martinez will return to Boston for another season before having the choice to opt out next winter.

This is a potentially big deal for the Red Sox, who get to keep arguably their best hitter -- but, possibly, at a steep cost.

Here are five things you need to know about Martinez's decision, including how it might impact their offseason plans with regards to Mookie Betts.

1. Martinez's decision makes sense

Martinez, 32, had another dominant offensive season in 2019, hitting .304/.383/.557 with 36 home runs in 146 games. He has been one of the game's top hitters since joining the Tigers and revamping his swing in 2014. Martinez owns an incredible .307/.373/.581 batting line in nearly 3,500 plate appearances the last six years. 

So why wouldn't Martinez want to hit the open market?

As a near full-time designated hitter on the wrong side of 30, Martinez and agent Scott Boras would have been taking a risk with the opt out. The market has not been kind to players with that profile in recent years. And while most players don't hit like Martinez, it's probably fair to think the downside outweighed the upside.

2. The Red Sox face uphill battle to get under luxury tax

The Red Sox have been public about their intent to get under the $208 million luxury tax threshold next year. Martinez opting in will not help the cause. He counts as $22 million against the team's luxury tax payroll. 

With Martinez in tow, the Red Sox are now about $57 million under the line. That number doesn't include arbitration raises or external additions. At this point, the Red Sox are projected to have more than $61 million in the former coming -- though that includes $11 million to Jackie Bradley Jr., who is likely to be non-tendered or traded. Even with Bradley Jr. elsewhere, the Red Sox will have precious remaining room to add free agents -- at least as currently constructed.

Nearly half of that $61 million is owed to Mookie Betts -- his projected arbitration prize is $27.7 million. That leads us to the next point.

3. Red Sox may look to trade Betts

The easiest path under the luxury tax line for the Red Sox was for Martinez to opt out. Now, Boston may look to trade Martinez. And, if they can't find takers for him, they may have to instead turn their attention to trading Betts.

Betts is one of the best players in baseball, but he has just a year of team control remaining before he hits free agency. If owner John Henry is more interested in saving money than winning ballgames, then moving Betts makes sense -- it would allow the Red Sox to improve their farm system and slash a healthy chunk off the budget in one swoop.

It should be concerning for the sport as a whole that one of the richest franchises in the league is entertaining trading an MVP candidate in order to avoid a trifling penalty -- the Red Sox paid less than $12 million in luxury tax fees last winter -- but unfortunately that's the reality of modern baseball.

4. Other veterans could be on the way out, too

Martinez and Betts aren't the only veterans likely to be shopped around. League sources told CBS Sports last week that Boston had been gauging interest in other players on their roster. That includes left-handed starter David Price, who counts for $31 million against the luxury tax but should draw interest from contenders, fringe and otherwise.

The Red Sox seem unlikely to find fair value for Chris Sale, and are highly unlikely to find takers for Nathan Eovaldi, Dustin Pedroia, or Rusney Castillo -- their high-salaried players who aren't Betts, Martinez, Price, or Xander Bogaerts.

As such, a fair expectation is that two of Martinez, Betts, and Price will be traded before the winter ends.

5. Martinez can opt out next winter

The Red Sox gave Martinez a five-year contract worth $110 million last February, and he helped the team to a World Series title later that year. Martinez's deal included opt-outs following the 2019 and 2020 seasons. 

Obviously Martinez passed on hitting the market this winter. It's too early to know whether he'll do the same next, but there's at least the chance that he's around only for one additional season.

Given the potential ramifications of Martinez opting in, that's probably not what Red Sox fans want to hear.

All free agents can begin signing with new teams Monday. Here are R.J. Anderson's top 50 free agents.