According to Ken Rosenthal of Fox Sports, those four teams are the Boston Red Sox, Chicago Cubs, Cleveland Indians and New York Yankees. That may seem like an odd set of teams to have on a no-trade list, but the article explained it as follows.
Often, players include high-revenue teams like the Yankees, Red Sox and Cubs in no-trade protection, thinking that those organizations are better positioned to offer financial inducements in an effort to convince the player to waive the clause.
Even without including those four teams, nearly every team has at least some level of interest in Upton as the 24-year-old is the type of player who can be a franchise cornerstone despite a down season this year.
He's coming off of a .289 BA, 31 HR, 88 RBI, 21 SB season last year, and is signed through 2015 for $38.5 million over the next three seasons. He is seen as a fairly cost-effective answer for the next several seasons.
The Rangers could look to pick him up as a replacement for Josh Hamilton, the Blue Jays have shown interest and the Braves have been named as a potential good fit. The Dodgers, White Sox and A's were also listed as teams that could make sense.
However, even with a deep market of teams interested in Upton, there is no doubt intrigue surrounding the teams on his no-trade list, both for Upton and for the Diamondbacks in terms of what they could net in return.
According to Diamondbacks GM Kevin Towers, the team is not necessarily looking for prospects, and he considers the club to still be in "win mode." The team has a clear need at third base and potentially at shortstop where Stephen Drew has a $10 million option for next season that could be declined.
So here is a look at how each of the four teams on Upton's no-trade list stacks up as a potential landing spot.
Boston Red Sox
The Red Sox are an intriguing trade partner for the Diamondbacks, as they have a shortstop prospect in Jose Iglesias and high-upside third base prospect in Xander Bogaerts, both of whom would be of interest to the Diamondbacks. They have a number of other developed prospects who could make an impact sooner rather than later that could be included.
The Red Sox have Cody Ross in right field on a one-year deal, and while he has produced well this season, the 31-year-old is not the team's long-term answer. Daniel Nava and Ryan Kalish have shown flashes, but Upton could fill the position long-term alongside Carl Crawford and Jacoby Ellsbury.
For Upton, the team provides him with a much bigger market to play in and a lineup loaded with star players that should result in immediately improved production.
As a rebuilding team, the Cubs don't seem like a team that would be willing to move their top young talent on the surface, but a 24-year-old outfielder signed through 2015 is exactly the type of player a team can build around.
A Starlin Castro-for-Justin Upton deal straight up is an interesting thought, but that may not be enough for the Cubs to pull the trigger on moving their young star.
On the prospect side, Josh Vitters has looked great in Triple-A this season and could prove to be an immediate upgrade at third base for the D-Backs, but the team may not be willing to put together a deep enough pool of prospects to make that deal.
The Indians pulled the trigger in acquiring the surprise name of the deadline last season, as they shipped their top two pitching prospects in a package of four young players to acquire Ubaldo Jimenez from the Rockies.
There is no question the team needs a right-handed bat, as their lineup is made up of seven left-handed hitters and two switch hitters, and Upton would give them a big boost.
However, I don't think the team has the pieces to put together a package that would beat out some of the aforementioned teams that have interest.
New York Yankees
The Yankees biggest need at the deadline is starting pitching, but they could stand to upgrade in the outfield this season and moving forward.
Curtis Granderson is entrenched in center field, but left field has been manned by a handful of veterans in the wake of an injury to Brett Gardner while right field has free-agent-to-be Nick Swisher and no real answer for next season.
The team has some intriguing prospects such as Mason Williams, Tyler Austin and Dante Bichette Jr, but those players are still a ways from big league contribution, and it does not look like the Yankees are a fit.