The group-stage game will proceed as scheduled on November 4 without Frankfurt supporters after the Prefect of Naples issued an order prohibiting Napoli from selling approximately 2,500 tickets to travelling fans.
Frankfurt had submitted a request to UEFA, the European governing body, to either move the game to a neutral venue or hold it behind closed doors, citing "safety and organisational deficiencies" at Napoli's stadium.
"The entirely different approaches from participating countries and national associations to high-risk matches... has now become a real problem for European fan culture and the integrity of European club competitions," the club's board member Philipp Reschke said in a statement.
"It's unacceptable that in most places, away fans are welcomed as a matter of course despite major challenges, while in others... away supporters are simply excluded by authorities in spite of identical circumstances and risks."
Frankfurt's complaints highlight a broader trend, with the club noting there have been 15 cases of official away fan bans in UEFA competitions since their supporters were first prohibited from Naples in 2023.
UEFA looking into adjusting regulations
The club added that UEFA had told them it is looking at changing the regulations in light of the rising number of bans, with Reschke saying the lack of away fans results in an "atmospheric and competitive disadvantage" on the pitch.
"UEFA regulations do not yet provide clubs who are unilaterally affected by official bans on away fans, or even the association itself, with any means of countering – or at least offsetting – this practice," Reschke added.
"Change will only be possible if the host clubs are given joint responsibility for official restrictions in future, and this way of dealing with security issues no longer unilaterally disadvantages visiting fans and visiting teams."
Reuters has contacted UEFA for comment.
Aston Villa said on Thursday that no away supporters would be allowed to attend their Europa League clash with Israeli side Maccabi Tel Aviv on November 6 after police raised public safety concerns about potential protests.
However, on Friday, British Prime Minister Keir Starmer said fans of the Israeli side should not be barred from the match in Birmingham.
UEFA said on Thursday that it "wants fans to be able to travel and support their team in a safe, secure and welcoming environment."
The governing body added that in all cases, "the competent local authorities remain responsible for decisions related to the safety and security of matches taking place on their territory.