MLB Trade Rumors: Potential Deals to Watch for Heading into 2019 Deadline

However, the list of sellers is not yet clear because a handful of teams are still within striking distance in the National League wild-card race. 

The American League has a clearer collection of sellers at the moment, with Detroit at the forefront, as it is trying to add more prospects to a young core in deals for its best players. 

Potential Deals to Watch

Kirby Yates to Boston

According to MLB.com's Jon Morosi, Boston is showing active interest in San Diego's Kirby Yates and Toronto's Ken Giles.

Orlando Ramirez/Associated Press

Even though the Red Sox have a plan at the moment to use Nathan Eovaldi as their closer, it would help to have some insurance in the bullpen as they attempt to hunt down the New York Yankees in the American League East, or go after a wild-card spot.

Six Red Sox pitchers have combined for 20 saves so far this season, and there is no guarantee Eovaldi slides into that role and makes it his since he is a converted starter.

That is why Yates makes sense as a potential addition via trade, as he would solidify the closer role and take pressure off Eovaldi, who could then become a setup man.

Yates has 31 saves in 41 appearances for the San Diego Padres, who are teetering on the edge of contention in the National League wild-card race. 

San Diego is five games out of the second NL wild-card position and has five teams in front of it on the outside looking in, including three from its own division. 

If the Padres believe they can't make a run at the postseason, they could collect assets to build on to their young foundation by dealing Yates. 

Back in June, MLB.com's A.J. Cassavell reported it would take an overwhelming offer to pry Yates from San Diego. 

The Padres' demands could be even higher since Yates comes with a year of team control for 2020, and they would want to maximize the return for one of the most coveted relievers on the market. 

Boston does not have the depth in its farm system to compete in an all-out bidding war, but if San Diego is willing to take a premier prospect or two, instead of a large sum of players, the Red Sox could get a deal done. 

While Eovaldi is a solid pitcher, the Red Sox would be smart to give him some support in their competition with Tampa Bay, Oakland and Cleveland for a wild-card spot. 

The price for Yates may end up being a bit high, but Boston should try its best to acquire him since the Padres closer could be the best reliever available.

Shane Greene to Philadelphia

According to NBC Sports Philadelphia's Jim Salisbury, the Philadelphia Phillies have had conversations with the Detroit Tigers about all of their available players, including pitchers Shane Greene and Matthew Boyd.

John Minchillo/Associated Press

Salisbury noted in his report that the Tigers were looking for more in return for Boyd since he comes with three years of control after this season.

The Phillies might not be willing to deal four young players, two of which have star potential and two others with a chance, which is the reported haul the Tigers want in exchange for Boyd.

The more realistic option for Philadelphia is to go after Greene to bolster a struggling bullpen that is currently headlined by Hector Neris, who has given up more earned runs than he has saves. 

Greene has 22 saves, which is four more than Neris, and he has recorded 40 strikeouts compared to 11 walks while earning a 1.25 ERA. 

If the Phillies want to create any type of advantage over St. Louis, Milwaukee, Washington and others in the NL wild-card race, they must make improvements to their bullpen. 

Greene possesses the shut-down ability in the back end of games that the Phillies are in need of, and he would come at a cheaper cost than Boyd because he has the single year of control after 2019. 

The Phillies could have a firsthand glance at Greene during their two-game series with the Tigers on Tuesday and Wednesday.

From Detroit's perspective, it should try to bring in as many young players as possible to continue its rebuild.

By trading for Greene, Philadelphia would improve its bullpen by not mortgaging all of its prospects in one deal, which could help it land a starter on a team that has lower demands than the Tigers do with Boyd. 

Nicholas Castellanos to Chicago Cubs

According to Chris McCosky of The Detroit News, the Chicago Cubs are among the ball clubs showing interest in Tigers outfielder Nicholas Castellanos. 

Carlos Osorio/Associated Press

Castellanos has 11 home runs, 36 RBIs, 34 doubles and an .822 OPS in 93 games for the struggling Tigers. 

The right-handed bat of Castellanos could provide balance to the Chicago Cubs order as they look to fend off challenges from Milwaukee and St. Louis in the NL Central. 

The 29-year-old has a 1.152 OPS, .387 batting average and only eight strikeouts in 72 plate appearances against left-handed pitching in 2019. 

Castellanos' ability to hit southpaws would provide the Cubs with an outfield option to rotate into the lineup for Kyle Schwarber or Jason Heyward, or a bat off the bench in late-inning situations. 

Chicago's team batting numbers are worse versus left-handed pitching, as it has a .242 batting average, .442 slugging percentage and .770 OPS, all of which are at least 10 points fewer than its totals against right-handed arms.

Schwarber only has 14 hits in 71 plate appearances against lefties, while Heyward is batting .200 with a .253 on-base percentage.

Since Castellanos is a free agent at the end of the season, he should have a lower price tag than his Detroit teammates due to lack of team control. 

The Cubs would likely still have to send one or two pieces back to the Tigers, but they might not be as significant as the prospects that potential deals for Boyd and Greene bring to Detroit.

Follow Joe on Twitter, @JTansey90.

Statistics obtained from Baseball Reference.