The club announced a new £24 million shirt deal with controversial moneylenders Wonga on Tuesday, and now the Muslim Council of Britain have attempted to intervene.
United have received widespread criticism after unveiling the four-year deal with the short-term loan company, and the MCB has now piled on further pressure.
Four Muslim players represented the club against Manchester United on Sunday – Demba Ba, Papiss Cisse, Cheick Tiote and Hatem Ben Arfa – and all are now being urged to make a stand.
Shaykh Ibrahim Mogra, assistant secretary general of the MCB, said: "There are two aspects to this. We have the rulings of the religious law and we have the individual's choice and decision on how they want to follow or not follow that rule.
"The idea is to protect the vulnerable and the needy from exploitation by the rich and powerful.
"When they are lending and are charging large amounts of interest, it means the poor will have short-term benefit from the loan but long-term difficulty in paying it back because the rate of interest is not something they can keep up with."
He added: "The Islamic system is based on a non-interest-based system of transaction."
The club did its best to offset criticism of the new deal by announcing that the Sports Direct Arena would revert to its original name of St James' Park, but it has not prevented MPs and large numbers of people through social media declaring their disgust.