2 prospects Mariners should trade at the deadline, 2 who should be off-limits

The Mariners head into the second half of the 2026 season with an uninspiring 48-49 record, their worst record through 97 games since 39-58 in 2019. And yet they remain favorably thought-of by the sports media. FanGraphs gives the M's the second-best odds to represent the AL in the World Series, while The Athletic has them as one of just seven teams which best met the criteria to win it.

Certainly, the Mariners remain one of the more talented rosters in baseball, plus they've dealt with several important injuries and a poor imitation of the real Cal Raleigh. At the same time there are still some needs, including relief help and a right-handed bat who can ideally hit lefties. Fortunately, the M's are in a better position than most when it comes to top-rated prospects, giving them some intriguing assets as the Aug. 3 trade deadline approaches.

2 top prospects Mariners should trade at 2026 trade deadline

Jonny Farmelo, OF

There's been plenty of success by Mariners prospects this season, but we would contend that Farmelo is the best story up to this point. After beginning his campaign slowly in High-A Everett, he started turning things around in May and then broke out in June, batting .309 with a 1.041 OPS and 164 wRC+. This tremendous form has continued into July, and has resulted in MLB Pipeline moving him up from 78 in their preseason rankings, to 64.

To many this is no surprise, for a player who the Mariners thought enough of to select 29th in the 2023 draft, so why have we included the 21-year-old as someone who should be traded?

As harsh as it may sound, this is about ongoing concerns about his health, after injury issues limited him to 75 total games over the past two seasons. To be clear, we'll be happy if he stays, but baseball is ultimately a business and it might be best for the M's to move him while his stock is rising, and before he potentially gets hurt again.

Felnin Celesten, SS

If Farmelo is the best Mariners prospect story this season, then his High-A Everett teammate Celesten is right behind him. At No. 71, he ranks lowest among M's prospects in MLB Pipeline's top 100, but he's having an outstanding campaign, batting .310 with a .932 OPS and 138 wRC+. At one point he went on a 25-game hit streak, which came within three games of the all-time Northwest League record.

So, why aim to move a player whose $4.7 million singing bonus in 2023 is the largest the Mariners have ever paid to an international player? There's some overlap with Farmelo in respect of injury concerns and selling high, but also because Celesten primarily defensive position is shortstop. There are many who consider the 20-year-old the organization's best infield defender behind Colt Emerson, but with Emerson effectively locked in as the prime shortstop long-term, the path to the majors in Seattle looks uncertain.

2 Mariners prospects who should be untouchable at 2026 trade deadline

Kade Anderson, LHP

The rise has been as rapid as it has been impressive, with Anderson dominating in his first year of pro ball. He leads all minor league pitchers with a 1.36 ERA and 0.688 WHIP, while also racking up 108 strikeouts over 72.2 innings in Double-A Arkansas. With a resume like this, it's no wonder the southpaw is the top pitching prospect in baseball as per MLB Pipeline.

Anderson deservedly got to pitch the opening inning for the American League roster in the Futures Game last Sunday and he took just 10 pitches to breeze through it, only giving up a bloop single. Triple-A Tacoma is calling, but the belief is it will only be a short stay. Bigger things beckon, and the recently-turned 22-year-old should be with the Mariners by Sept. 1 at the latest.

Ryan Sloan, RHP

Anderson is the more polished player at this stage, but Sloan is seen by many as having the higher ceiling, with Baseball America ranking him as the top pitching prospect in baseball. This has led to debates about who is better, which is the best kind of 'problem' for the Mariners to have. A rotation which has been among the best in the majors in recent years, should maintain this position moving forward thanks to the young duo.

The 20-year-old has been a bit more up and down with his form, with a 4.04 ERA and 1.187 WHIP with 77 Ks across 62.1 innings in Double-A Arkansas. However, he does seem to bring it more than Anderson when the spotlight shines brighter, including in the late-March Spring Breakout game against the Brewers and during the Futures Game. Sloan is also in the running to be called up by the Mariners this season, but there is a possibility he'll be held back until next year to allow him more time to develop.

* We did not include Lazaro Montes as an untouchable, as much as we don't believe the Mariners want to or should move him. However, he's the perfect guy to keep available just in case, if the right trade presents itself.

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