The 19th episode of 'Chicago Fire' will film the week of Feb. 23.

NBC's Chicago Medical spinoff is beginning to take shape.

Sources tell The Hollywood Reporter that the potential medical-themed spinoff will air as the 19th episode of Chicago Fire and hail from the Chicago team of Dick Wolf, Matt Olmstead, Derek Haas and Michael Brandt.

The episode will focus on characters who work at the Chicago Medical hospital and be integrated into Fire in the same fashion that previous spinoff Chicago PD took shape.

While Chicago Medical, from Universal Television, is not a formal pilot order, NBC could opt to use the episode as such when considering whether or not to move forward with a third show in the franchise.

Both Chicago Fire and Chicago PD have been solid performers for NBC, with both shows helping reinvigorate the procedural at the broadcast network.

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Sources tell THR that Fire is currently casting for seven guest-star roles with a series option:

• A new candidate for a Chicago fireman in his 20s.

• A reformed alcoholic and fireman whose humor covers his demons, described as a brooding and mysterious guy in his 30s or early 40s.

• Nurse Kayla Goodwin, a smart girl who went to school with Taylor Kinney's Kelly Severide and is his potential love interest.

• A new doctor (male or female) who could anchor the medical show and potentially serve as the head of psychiatry.

• A head of pediatrics (male or female)

• An admissions nurse (male or female)

• A female paramedic described as dirty and edgy and not the all-American blonde type.

The news comes weeks after NBC Entertainment chairman Bob Greenblatt told reporters at the Television Critics Association's winter press tour that Chicago Medical was "something we're just seeding into the system" and "seeing if there's a show there that could eventually spin off into itself."

"It's a bit of an experiment to see how those characters come out," NBC Entertainment president Jennifer Salke said at TCA. "[Dick Wolf] had such a good run with the crossover episodes and created a world that moves around, with these shows that move around each other. I think it's natural that he wants to create a medical component to that. He looks at will the paramedic stories and fire butt up against that? I think it's sort of an organic way to see if it feels like it can sustain its own show."

Should Chicago Medical move to series, it could be Wolf's fourth show on NBC, joining both Fire and PD as well as veteran Law & Order: SVU, should all three earn renewals for the 2015-16 season. Greenblatt previously noted that "the odds are great" that both PD and Fire will return.

Medical fare has been one of the biggest priorities for the broadcast networks this past development season as many look for fresh takes on the genre. There are four other medical-themed drama pilots already in the works this season: ABC's The Advocate, CBS' Code Black and LFE as well as NBC's Heart Matters.

Email: Lesley.Goldberg@THR.com

Twitter: @Snoodit