DENVER -- The Pirates didn’t call anyone up from the Minor Leagues on getaway day in Denver on Sunday, but they are expected to add players following the end of Triple-A Indianapolis’ regular season Monday. Pittsburgh opens its next series Tuesday against the Marlins at PNC Park.

The Pirates’ one roster move Sunday was to activate reliever Clay Holmes off the injured list.

There are some intriguing storylines with potential callups as the active rosters expand from 25 to 40 players in September. At the forefront is whether third baseman Ke’Bryan Hayes, the organization’s No. 2 prospect, according to MLB Pipeline (No. 36 overall), will be at PNC Park on Tuesday. Hayes struggled earlier this season at the plate but had a resurgent August, perhaps opening the door to a September promotion.

The obvious candidates for callups are middle infielder Cole Tucker, infielder/outfielder Kevin Kramer (Pirates’ No. 9 prospect) and outfielder Jason Martin (Pirates’ No. 16 prospect). Pittsburgh also needs an emergency third catcher; Steven Baron and Christian Kelley are the candidates there.

The bullpen is an area in need of reinforcements. Several relievers could be called up, including Luis Escobar, Yefry Ramírez, Montana DuRapau, Parker Markel, Alex McRae, Dovydas Neverauskas, Yacksel Ríos and Rookie Davis.

Here’s a look at some notable prospects who have either arrived this season or could be arriving this month, as well as prospects to watch as they continue to develop in the Minors.

Arrival: Bryan Reynolds

It took a series of injuries in the outfield, but the Pirates called up Reynolds on the same day as Tucker after a collision that sent both Starling Marte and Erik González to the injured list. Tucker was eventually sent back down, but Reynolds forced the Pirates to keep him in the Majors with his consistently excellent play. Now, the switch-hitting rookie is a candidate to win the National League batting title and he’s likely to find his name on NL Rookie of the Year ballots.

Top prospect Mitch Keller is also in the big leagues to stay as he auditions for a spot in the 2020 rotation. Former first-round Draft pick Kevin Newman graduated from rookie/prospect to everyday shortstop. Tucker, Martin, Kramer and Escobar made cameos in Pittsburgh earlier this season, and they’re bound to return soon.

Breakout: Cody Bolton

There are a number of interesting prospects on the rise in the Pirates’ system, including steady outfielder Jared Oliva, speedy shortstop Ji-Hwan Bae and home-run/RBI machine Mason Martin. But keep an eye on Bolton, who is ranked as the Bucs' No. 13 prospect.

Bolton had some uneven performances between his promotion to Double-A Altoona and the point when he reached his innings limit. But the 21-year-old right-hander – a sixth-round pick out of high school in 2017 – dominated for Class A Advanced Bradenton this season. In 12 starts for Bradenton, Bolton posted a 1.61 ERA and 0.86 WHIP with 69 strikeouts in 61 2/3 innings. Bolton is a few years away, but he is worth watching.

Something to prove: JT Brubaker

This has nothing to do with performance and everything to do with health. Coming out of Spring Training, Brubaker looked like part of the Pirates’ top Major League-ready rotation depth in Triple-A Indianapolis. He made only four Triple-A starts and two low-level rehab outings because of a forearm/elbow injury, and he is still working his way back while playing catch on flat ground.

The Pirates will need rotation options, even depth, next season. Brubaker needs only to prove that he’s healthy and still ready for the next level.

Name to watch: Oneil Cruz

It’s hard not to watch Cruz, the 6-foot-6 shortstop who earned a midseason promotion to Double-A Altoona. He’s a special talent and a unique player, even if he is raw and at least a year or two away from Pittsburgh.

As Altoona manager Michael Ryan put it: “He just does one thing a day where you’re like, ‘Holy cow, not everybody can do that.’ Then there are also reminders each day that he’s only 20.”

Cruz, who probably has more upside than anyone in the Pirates’ system, will spend time in the prospect-loaded Arizona Fall League this offseason. Will he stick at shortstop? Will his tools translate into consistent production? Assuming he returns to Double-A to begin the season, how aggressively will the Pirates move him up the ladder next year?