He will become the latest high-profile player traded away by the Mariners, who are tearing down their roster in an effort to rebuild the team.
Segura, 28, hit.304/.341/.415 with 29 doubles, 10 homers, 20 steals and 91 runs last season.
That's why it shouldn't come as a surprise to hear that the team's first big move of the offseason is expected to be one of many.
The deal will include multiple players and Segura will need to waive his no-trade clause.
Nicasio, who threw two games for the Phillies in 2017 after getting claimed off waivers by the Pirates, and Pazos are bullpen pieces, but it's Segura that is the centerpiece of the deal for Philadelphia. How about Santana? Why are they giving up on him so early in his contract? Segura is regarded as an above-average defender, meaning he should help the Phillies' porous defense.
The Mariners would likely receive J.P. Crawford in return.
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Crawford, selected by the Phillies in the first round (16th overall) of the June 2013 draft, appeared in 72 games for the Phillies over the last two seasons and slashed.214/.333/.358 over 225 plate appearances.
Crawford, 23, has appeared in 72 Major League Baseball games with the Phillies over the past two seasons.
"Carlos Santana has been among the most durable players in the big leagues over the last eight years and has been a fixture in the middle of lineups during that time", Mariners general manager Jerry Dipoto said in a press release.
While the deal immediately improves Philadelphia's roster, what does it mean for the Phillies in relation to the Harper and Machado sweepstakes?
Manny Machado #8 of the Los Angeles Dodgers slides safely into third base after hitting a triple in the seventh inning during a game against the Philadelphia Phillies at Citizens Bank Park on July 23, 2018 in Philadelphia, Pennsylvania. Adding Segura to the picture still leaves the Phillies options if Machado chooses the City of Brotherly Love.