Luis Castillo made his first All-Star appearance this year at age 26. He’s in only his second full season with the Reds and on track to become a free agent after the 2023 season. Entering play Tuesday, he ranked fifth in the Majors with a 2.41 ERA, while earning near the Major League minimum.

In short, he’s one of the most valuable players in baseball, in both performance and cost effectiveness.

With regard to Castillo, the Reds can approach the upcoming Trade Deadline in one of two ways. The first is to categorically rule out any notion of a trade, making clear that he’s a non-negotiable part of the team’s future. The second is to attach an exorbitant price tag to his dynamic right arm and see if any general manager has the gumption to pay it.

At least for now, sources say, the Reds are taking the latter approach -- particularly since there’s no public evidence to suggest Castillo is on the verge of signing an extension with the club.

Castillo is not “available” in a practical sense of the term, and yet the Reds haven’t hung up the phone on teams who have called. They are waiting to be wowed, while feeling content to open 2020 with a largely unchanged pitching staff.

The Reds’ current starting five -- Castillo, Sonny Gray, Tanner Roark, Tyler Mahle and Anthony DeSclafani -- have combined to start all but one game for Cincinnati this season. Of that group, only Roark is eligible for free agency this winter.

Collectively, the Reds’ rotation ranked fourth in the Majors with a 3.75 ERA entering Tuesday.

So, why consider changing it?

There’s logic in listening to offers for Castillo, only if the Reds can acquire a Major League-ready starter and improve at least one (and probably two) positions in the team’s long-term lineup.

The Braves are known to be pursuing starting rotation upgrades. A credible offer for Castillo would need to begin with outfielder Cristian Pache -- the Braves’ No. 1 prospect, according to MLB Pipeline -- and right-hander Ian Anderson, a 21-year-old who is maintaining a 2.91 ERA at Double-A Mississippi this season.

The Padres could pair a corner bat from their Major League club (Franmil Reyes or Hunter Renfroe) with one pitcher from the group of Luis Patino, Adrian Morejon, Ryan Weathers and Logan Allen. It would be difficult to imagine the Padres parting with their No. 1 prospect, left-hander MacKenzie Gore, but No. 2 prospect Luis Urias could be an intriguing fit for the Reds in lieu of Reyes or Renfroe.

The Dodgers aren’t desperate to acquire Castillo, as they already have the National League’s best rotation ERA, but the Dodgers would have the wherewithal to make a compelling offer. Right-hander Dustin May, shortstop Gavin Lux and a top catcher -- Keibert Ruiz or Will Smith -- likely would cause the Reds to consider moving Castillo, although there’s no indication the Dodgers are prepared to go that far.