The duo played together on the Yugoslavia national basketball team from 1986 to 1990 and were at one time close friends, but the Yugoslav Wars drove them apart emotionally, as they came from opposing sides.

[6] Michael Tully of hammertonail.com sees the film as "being about many different things at once—a history lesson, a touching interpersonal drama, and a positive reaffirmation that the American Dream still exists and isn't a completely silly construct" and labels it "a very strong work, in which the grand scope of the Yugoslav Wars of the early 1990s is personalized through the relationship—and unfortunate falling out—between former NBA stars Vlade Divac and Dražen Petrović".

[8] Writing for the Slant Magazine blog, Jason Bellamy summarizes Once Brothers as an intimate tale that paints a vast panorama, but sees its long intro as necessary because "a good number of average [American] sports fans might not even remember Divac and Petrovic, and even many legitimate NBA fans are unlikely to know much about that duo's European careers, not to mention the outline of the war in the former Yugoslavia".

Divac and his former Yugoslavian teammates express all of the obstacles that are in the way for a foreign-born player, including style of play, language and the lack of belief by others that they could actually cut it in the NBA".

Club, Scott Tobias had mixed feelings about the movie: "For all its earnestness and nobility, Once Brothers is still very much an NBA Entertainment production, following Divac's 'journey' to a conclusion that's as disappointingly precooked as a VH-1 Behind The Music special".

He continues by saying the film has a great story, but that it's also "framed in a contrived way with Divac telling us that his eldest son, an 18-year-old, wants to know what life was like when he was his age, and so into the Wayback Machine we go".

Tobias ends by saying the scene with Divac walking through Zagreb is the best one in the entire movie, but that it also has a problem of being "just another step in Divac's scripted road to reconciliation, which ends predictably with a casual conversation with Petrovic's mother and a visit to his friend's grave", before concluding that "Once Brothers has some moving scenes despite itself, but the whole production feels as spontaneous as a frozen pizza—just heat and serve".

[12] Croatian media generally complained over the omission of Stojko Vranković, a close friend of Petrović's, who, unlike Divac, was in constant contact with him throughout 1991–1993.

Vranković, who suited up for Yugoslavia in four major competitions (all four with both Divac and Petrović as teammates) and whose two seasons in the NBA overlapped with both players' time in the league, did not watch the movie.

Though confirming the national team functioned like a family, he also disputed the friendship and closeness between Petrović and Divac: "Stojko Vranković was Dražen's best friend.

[18] Zoran Čutura, a four-time participant in major competitions with Yugoslavia (three of those coming with both Divac and Petrović) refused to watch the movie, opining that it's "pointless, needless, and meaningless" while adding: "Personal friendships and internal relations within a sports team are a category that's very difficult to grasp and understand for an outsider, and I see no point in trying to explain them rationally.

Many things happened in the calendar of our lives since then, and explaining player relations, chemistry and circumstances that this team, which was unique in every way, functioned in is lacking common decency, especially when it's done from an American perspective".