The Kansas City Royals are unloading veterans as they embrace what it essentially a free agency forced rebuild.

Monday night, the Royals continued the tear down with a four-player trade with the Oakland Athletics. First baseman Brandon Moss and lefty reliever Ryan Buchter are going to the A's in exchange right righty Jesse Hahn and pitching prospect Heath Fillmyer. Both teams have announced the trade.

Moss, 34, is entering the second year of a two-year contract worth $12 million. He'll make $7.25 million in 2018 before a $10 million club option comes into play for 2019 (with a $1 million buyout). Moss hit .207/.279/.428 (84 OPS+) with 22 home runs in 118 games for the Royals last season.

The A's already have Matt Olson at first base as well as a full outfield (Matt Joyce, Boog Powell, Stephen Piscotty) and an occupied DH spot (Khris Davis), so it's likely Moss will have to settle for a part-time platoon role in his second stint in Oakland. He played for the team from 2012-14, hitting 76 homers in three seasons.

MLB: Kansas City Royals at Detroit Tigers
The A's have brought Brandon Moss back in a trade with the Athletics. USATSI

Buchter gives the A's a second left-hander reliever alongside the underrated Daniel Coulombe. The 30-year-old southpaw went from the Padres to the Royals at the trade deadline last year and finished the season with a 2.89 ERA in 65 1/3 innings. He owns a 2.88 ERA with 143 strikeouts in 128 1/3 innings since breaking out with San Diego in 2016.

The Royals are happy to unload Moss' salary, of course, but this deal is more than a salary dump. Hahn, 28, has potentially, though he had trouble staying healthy with the A's the last few seasons, throwing 212 2/3 innings with a 4.57 ERA (89 ERA+). He will compete for a rotation spot in spring training.

Fillmyer, 23, threw 149 2/3 innings with a 3.49 ERA at Double-A last season. MLB.com ranked him as the 18th-best prospect in Oakland's system before the trade, saying "has the ingredients to become a No. 4 or 5 starter in the big leagues."

A few weeks ago the Royals unloaded relievers Scott Alexander and Joakim Soria in a three-team trade with the Dodgers and White Sox. They've already lost Lorenzo Cain to free agency -- Cain signed a five-year deal with the Brewers last week -- and they're likely to lose Eric Hosmer and Mike Moustakas as well. Here is Kansas City's tentative lineup at the moment:

The big league roster isn't looking so great and, earlier on Monday, Baseball America ranked the Royals' farm system as 29th best in baseball. Kansas City has a long way to go to get back to contention. Trading Moss, Alexander, and Soria are just the first few steps in the rebuilding process.