Private Red Sox buzz could give Mariners second chance at major target

In a wild twist nobody saw coming, the Seattle Mariners, who entered the 2025 season desperate for answers at first base, suddenly find themselves in a good spot. The short-term problem is solved with the addition of Josh Naylor, whose bat has immediately bolstered Seattle’s playoff hopes.

And now, a new wrinkle from the East Coast could put a former Mariners target back on their radar — and at a bargain, no less.

Triston Casas, once rumored to be part of a blockbuster trade proposal for Luis Castillo, could quietly be on the market. According to Chris Cotillo of MassLive, the Boston Red Sox were “especially intrigued” by Tampa Bay Rays first baseman Yandy Díaz ahead of Thursday's trade deadline due to his team control beyond 2025. But more telling is what Cotillo reported next:

 “Privately, the club is not guaranteeing that Triston Casas, who is rehabbing from a season-ending knee injury, is guaranteed to be the starter in 2026.”

Red Sox rethinking Triston Casas role opens door for Mariners buy-low move

Let’s pause there. That’s a massive development for a player who was once viewed as a future cornerstone in Boston. It also suggests the Red Sox are no longer banking on Casas returning as the same slugger. And it cracks the door open for the Mariners to revisit a player they once thoroughly evaluated.

It’s worth remembering how close Seattle was to making a move. As Adam Jude of The Seattle Times reported during the offseason, “The Mariners, by all accounts, did a deep dive. They did their homework. At the end of the day, they came to the conclusion that [Casas] wasn’t a great fit for T-Mobile Park.”

In hindsight, that decision looks wise. Casas is going to miss nearly all of 2025 due to a knee injury. There’s no way of knowing if the same fate would’ve awaited him in Seattle, but it’s fair to say the Mariners dodged a bullet by not moving Castillo.

Still, this isn’t about hindsight, it’s about opportunity. The Red Sox are no longer treating Casas like a foundational piece. And while they may not be openly shopping him, his name no longer seems untouchable. That’s where a club like Seattle can take advantage.

Casas remains a high-upside bet. In 2023, his first full season in the majors, he gave the Red Sox a glimpse of what made him so intriguing by slashing .263/.367/.490 with 24 homers and 65 RBIs in 132 games. But injuries have stalled that trajectory. Since then, he’s struggled to stay on the field.

If the Red Sox are truly open to controllable upgrades at first base, and Casas is no longer seen as a lock for the future, it sets the table for a potential steal.

The Mariners don’t need Casas the way they did six months ago. But that’s exactly what makes this an ideal moment to strike. With Naylor set for free agency at the end of this season, Seattle could look to buy low on Casas in the offseason. No pressure. No rush. Just an investment in upside.

If he hits, suddenly the Mariners have an embarrassment of riches at first base. And if he doesn’t? The cost likely won’t break the farm.

This is how savvy front offices stay ahead. And with the Red Sox reevaluating their future and the Mariners now solid at first base, a quiet buy-low move for a former top-30 prospect could wind up being one of the savviest plays Jerry Dipoto has made yet.