Former European Cup winners Red Star struggled against modest Icelandic outfit IBV in the Europa League second qualifying round and barely deserved their 2-0 aggregate win, prompting manager Slavisa Stojanovic to rebuke his players after Sunday's training session.
"All the hard work you have done in the searing heat of pre-season build-ups will amount to nothing if you keep eating meat pies before practice and drinking two or three beers after it," Stojanovic was quoted as saying by Belgrade media on Monday.
"You have to rest properly and adopt an athletes' diet otherwise your careers will go down the drain," he said.
Red Star vice-president Nebojsa Covic added: "Cigarettes and nights out on boat-bars lined up along the river are also out of the question. A professional attitude means turning up for practice and raring to go an hour before it starts."
Red Star have not survived the winter break in European competition since 1992 and have also relinquished their domestic supremacy to bitter city foes Partizan, who won a record sixth successive league title last season to equal Red Star's overall tally of 25.
Paparazzi and Serbian tabloids have occasionally produced photos of first division players revelling in Belgrade's entertaining nightlife, including drinking and smoking in popular bars along the city's two rivers, the Sava and the Danube.
In January, Red Star's Montenegrin defender Milan Jovanovic was sent home from mid-season training in the Turkish resort of Antalya after he was caught in an all-night drinking stupor. He parted company with the club by mutual consent in April.
Goalkeeper Boban Bajkovic, who rescued Red Star in the 0-0 return leg draw against IBV when he made several key saves, including a late penalty, acknowledged that Stojanovic had every reason to ring the alarm bells.
"He didn't target anyone in particular but addressed the team on what our future attitude should be like," said Bajkovic. "We are all professionals and we ought to know how to behave.
Red Star are away to Ukraine's Chernomorets Odessa in the first leg of their Europa League third qualifying round on Thursday.