With the calendar flipping to 2019, the majority of teams in baseball are gearing up to follow in the footsteps of the Boston Red Sox and become the next World Series champions.

While some clubs, such as the Philadelphia Phillies, Cincinnati Reds, and St. Louis Cardinals have already made moves to improve, others are moving in the opposite direction in an attempt to prepare for the future.

Here are five teams that will take a step back from last season and perform worse in 2019.

Seattle Mariners

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The Mariners are going to look drastically different from the club that won 89 games last season.

General manager Jerry Dipoto has already traded five of Seattle's most valuable players, including James Paxton, Robinson Cano, Jean Segura and Edwin Diaz, while also letting Nelson Cruz depart in free agency.

Dipoto's "re-imagining" of the roster included the addition of Japanese import Yusei Kikuchi to the starting rotation, as well as Edwin Encarnacion and Domingo Santana into the lineup.

Encarnacion, though, may not be long for Seattle, as the Mariners are reportedly confident they'll trade him before spring.

Despite some positive moves, this still appears to be a team that will struggle to match last year's output. It could be a very long season in the Pacific Northwest.

Arizona Diamondbacks

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Trading a franchise cornerstone and letting a Cy Young contender leave via free agency doesn't normally lead to improved results.

That's the situation the Diamondbacks have put themselves in after dealing Paul Goldschmidt to the Cardinals and watching Patrick Corbin sign with the Nationals. Goldschmidt was one of the league's most valuable players last season, accruing 5.1 fWAR (as measured by FanGraphs) and Arizona doesn't seem eager to replace his bat in the lineup.

Meanwhile, there's a gaping hole at the top of their rotation after Corbin inked a new six-year deal with Washington. The left-hander placed fifth in NL Cy Young voting last year, authoring career bests with a 3.15 ERA and 2.47 FIP while striking out over 11 per nine innings.

After finishing 82-80 last season with Goldschmidt constructing another MVP-caliber campaign, the Diamondbacks should slide further in 2019. Especially if they also trade Zack Greinke, as has been rumored.

Oakland Athletics

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It's hard to predict how the Athletics will do in any given season, and 2019 is no different.

On paper, they look similar to the team that made the postseason last year. But a rotation that already featured multiple journeymen is now weaker after Trevor Cahill departed for a free-agent deal in Anaheim, and All-Star second baseman Jed Lowrie may also be gone after the Athletics acquired Jurickson Profar. Staff ace Sean Manaea is also likely to miss the majority of the season after requiring shoulder surgery.

The bullpen should continue to be a strength, though rental Jeurys Familia returned to the Mets in free agency. The lineup still carries the impressive duo of Khris Davis and Matt Chapman, but coming close to the 97 wins of 2018 will be a difficult task for the Bay Area squad.

Toronto Blue Jays

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The rebuild is on in Toronto.

Unlike the other teams on this list, the Blue Jays were not contenders last season, but Toronto still enters 2019 with a squad that looks very different from years past.

Josh Donaldson, Troy Tulowitzki, and J.A. Happ are gone, while Marco Estrada will likely land a deal with a new club in free agency. The remaining veteran pieces - Justin Smoak, Russell Martin, and Kendrys Morales - may serve as trade chips as the season progresses.

Recently acquired Matt Shoemaker and Clayton Richard will help fill out the rotation and hopefully serve as a placeholder for some of their younger arms, but there's a lot of work to be done before the Blue Jays return to contention.

Vladimir Guerrero Jr. should add some excitement and ease a bit of the pain next season, but expect Toronto to have one of baseball's worst records in 2019.

Cleveland Indians

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With the Indians positioned to win another AL Central crown, their front office made some questionable moves this offseason.

In an effort to reduce payroll and keep a winning product on the field, they traded Encarnacion, All-Star catcher Yan Gomes, and first baseman Yonder Alonso, and brought back former Indian Carlos Santana and added Jake Bauers in trades. Even further, Cleveland is dealing with the loss of both Andrew Miller and Cody Allen at the back end of the bullpen.

Only the Minnesota Twins appear to stand a chance of challenging Cleveland in one of MLB's weakest divisions, so the Indians should be fine even if they lose a few more games.

If things don't go well to begin the year, though, it could be the end of Corey Kluber's incredible run in an Indians uniform. While Cleveland is reportedly unlikely to deal the two-time Cy Young winner anytime soon, he has been a frequent subject of trade discussions and would be a perfect deadline add for a contender.