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NASHVILLE, Tenn. - The fourth team in the blockbuster – or, at least, in some permutations of the blockbuster – is Seattle.

And the Mariners, in the opinion of one of the officials involved in the talks, amount to the biggest roadblock, unsure of whether to push forward with the deal.

Texas general manager Jon Daniels is the driving force behind the trade, feverishly trying to land Arizona right fielder Justin Upton, according to multiple sources. Cleveland is the third principal team in the deal.

Daniels’ desire to land Upton could indicate that the Rangers would prefer not to re-sign free-agent outfielder Josh Hamilton, and may be confident of landing free-agent right-hander Zack Greinke.

But barring a major shift in the talks, the four-team blockbuster appears unlikely to happen, sources say.

The teams in the trade have discussed numerous combinations of players, and the identity of the fourth team has shifted at various points. Tampa Bay was involved at one stage, sources say, and so was Kansas City, according to ESPN.com.

Shortstop Asdrubal Cabrera is a linchpin of the deal, going from Cleveland to Arizona. The player that Seattle wants most is left-hander Derek Holland, sources said.

The package of young players going to Cleveland would vary, but Arizona right-hander Trevor Bauer, left-hander Patrick Corbin and Texas infielder Mike Olt were among the names in play, according to one source.

Seattle also would give up prospects, and club officials are divided over whether the team is in a strong enough position competitively to make such a deal, the source said.

-Ken Rosenthal