Xander Bogaerts, SS, Red Sox
Under club control through 2022
(signed through 2025, opt out clause after 2022)

J.D. Martinez, OF/DH, Red Sox
Under club control through 2022

Bogaerts has an opt-out clause in his contract that he is expected to exercise, which would make him a free agent at the end of this season. He’s slashing .323/.393/.473 through his first 50 games, though that hasn’t helped the Red Sox, who entered Friday at 24-27, 12 games behind the AL East-leading Yankees. Bogaerts plays an excellent shortstop and will be highly sought after by a number of teams if the Red Sox decide to become sellers.

Martinez entered Friday with an AL-best .360 batting average and a .976 OPS, and while he clubbed only five home runs during his first 42 games, he remains one of the most consistently reliable hitters in the game. Now that the NL is utilizing the DH, the group of potential suitors is twice as big as it was before. Martinez is earning just north of $19 million this season, the last of his five-year, $110 million deal with Boston.

If the Reds decide to trade Castillo this offseason, a reasonable ask would be one top prospect who is also a top 100 prospect in baseball, and one other prospect inside a team’s top 10.

For the Mets, Francisco Alvarez and Brett Baty will be off-limits in pretty much any trade. So inquiring teams can forget those two.

That means that for Castillo, a fair offer from the Mets could be SS Ronny Mauricio (ranked No. 3 on SNY’s Top 20 Mets prospects list and No. 53 on the MLB Pipeline Top 100) and RHP J.T. Ginn (ranked No. 5 on SNY’s Top 20). And the Mets would need to sign Castillo to an extension to make that deal worthwhile.

One issue with the above could be the fact that the Reds have highly thought of SS prospect Matt McLain, who could make his MLB debut in 2023. But Mauricio might wind up at third base or second base long-term.

If the Reds are seeking an outfield prospect or first base prospect who’s close to the majors in any deal for Castillo, the Mets might not be a fit as a trade partner.