Serbian club Novi Pazar said some members of their delegation were attacked by a group of masked men outside a restaurant the night before Thursday's second leg of their Conference League qualifier at Polish side Jagiellonia Bialystok.

About 15 men in balaclava masks moved towards the delegation when they were leaving a restaurant in central Bialystok, which caused them to retreat and call the police, Novi Pazar said in an Instagram post on Thursday.

The delegation were later attacked by a group of 30 people in masks when they tried to get into a vehicle, the club said in a statement.

"We would like to point out that our members were not wearing any club insignia ... Only thanks to the composure of those present and, at that moment, the professional reaction of the police officers, serious incidents were avoided," they added.

"The Novi Pazar Football Club expresses its deep concern for the safety of its members and its indignation at the slow reaction of the local police."

Novi Pazar said they would not attend a pre-match joint lunch, planned for Thursday according to UEFA protocol, due to the incident the previous night.

UEFA, Jagiellonia and Bialystok provincial police were not immediately available for comment.

Novi Pazar, who lost the home leg 2-1 last week, have travelled to Poland with a large delegation including players, staff, management, sponsors and friends of the club.

"We also hereby ask all supporters and fans of the club who will attend tonight's match individually not to wear club insignia, in order to avoid any kind of incident and maintain the safety of all those present," Novi Pazar added.

Polish media reported last week that hundreds of Novi Pazar fans gathered in front of the hotel where the Jagiellonia players were staying before the first-leg clash, chanting and setting off fireworks. REUTERS