Newcastle's sponsorship deal with loan company Wonga could prove contentious with the club's Muslim players, a religious organisation has warned.
The Muslim Council of Britain (MCB) has stated that wearing shirts with Wonga's logo on could infringe Islamic law, placing some of the club's players in difficulty.
But they have denied telling the players not to wear the shirts and said it will be up to them to decide what they do.
In their last game, Newcastle fielded four players who are practising Muslims - Hatem Ben Arfa, Demba Ba, Cheick Tiote and Papiss Cisse.
Shaykh Ibrahim Mogra, assistant secretary general of the MCB, said Islamic law teaches that earning interest on money is not allowed.
He said: "Islam does not treat money like a commodity that you can trade like food or clothing. For example I cannot lend £100 and then take back £120.
"But there is a distinction between the religious law and the choice of the individual.
"The MCB has not been in touch with the four players or the football club, we simply put the Islamic position to the people and then it's up to them how they behave
"And in terms of football it's not just about loan companies but about betting or alcohol companies.
"I'm calling for sporting organisations and the Government to have a debate about this and see where we should draw the line on advertising in sport."
Mogra referred to the example of former Tottenham striker Frederic Kanoute, who requested not to wear the 888.com logo of the gambling website when he played for Seville in Spain.
This was because of his religious beliefs and Mogra said it was important that players' wishes were honoured.
The decision to agree sponsorship with Wonga has also caused controversy elsewhere, with MPs and other leaders in the north-east calling it irresponsible.
Yesterday, Nick Forbes, leader of Newcastle City Council, said he was "sickened" and "appalled" that the club had signed the deal.