As the Mariners traded off high-priced veterans last offseason, they had one player who was thought to be immovable due in part to a “poison pill” in his contract — third baseman Kyle Seager.



No longer is a trade of Seager unrealistic.



With the demand for third basemen exceeding the supply, multiple teams are showing interest in Seager, according to major-league sources.



Seager, 32, would be an option for the teams that miss out on Anthony Rendon and Josh Donaldson in free agency and the Cubs’ Kris Bryant in a trade. At least five clubs — the Nationals, Braves, Rangers, Dodgers and Twins — are considering upgrades at third base.



The “poison pill” in Seager’s contract is a $15 million club option for 2022 that converts to a player option if he is traded, increasing his guarantee over the next three seasons to $52 million.



A year ago, with Seager coming off a career-low .673 OPS and owed a...