(CNN) -- English Premier League club Newcastle United and striker Papiss Cisse are at odds over the club's sponsorship deal with a finance company, according to the player's agent.
Cisse, who terrorized opposition defenses when he moved to soccer's Premier League last year, hasn't been included in Newcastle's squad for a pre-season tour of Portugal, the team from Northeast England revealed on its website
A Muslim, Cisse doesn't want to don Newcastle's jersey -- according to his agent -- because the sponsor is Wonga, which, as stated on its website, lends money with an annual interest rate of more than 5,800 percent.
"He feels that it is immoral....," the Senegal international's agent Madou Diene told CNN, outlining his interpretation of the striker's position.
Diene declined CNN's request to interview Cisse.
Earlier this month UK consumer watchdog Which? revealed a million families a month needed short-term high interest loans to get by.
Of those, 400,000 used the cash to pay for essentials such as food and fuel, while a further 240,000 needed money to pay off existing debts.
Newcastle, which did not return calls from CNN seeking comment, has yet to explain why Cisse did not travel with the squad to Portugal.
Under Sharia law, making money from interest, for example, isn't allowed.
But the BBC reported that two of Cisse's Muslim teammates, midfielders Cheick Tiote and Moussa Sissoko, told the club they had no issue with wearing the shirt and both of them were included in the squad for the trip to Portugal as the club prepare for the new English Premier League season which starts on August 17.
The partnership between the club and Wonga is said to be worth $38m over four years.
Wonga, which declined comment on the Cisse case, launched its first website in 2007 and according to its website, "rapidly became one of the world's most innovative credit providers."
For first-time users, loans of up to about $600 can be requested and Wonga usually provides an answer, it says, in seconds.
However, the interest such companies charge consumers has raised concerns among a number of British politicians.
"Urgent action is needed to grip the regulation of the payday loan industry, as the number of cases of misery and hardship are growing rapidly because of pressures on living standards and personal finance," Chris Leslie MP, Labour's Shadow Treasury Minister, told the British opposition party's website in June.
Cisse wore Newcastle's jersey last season when it was sponsored by another finance company -- lender Virgin Money.
"I guess it might be a question of people's views changing over time," Shaykh Ibrahim Mogra, assistant secretary general with the Muslim Council of Britain, told CNN.
"Maybe they've not had a chance to think things through beforehand. Maybe now they realize," added Mogra in response to the question as to why Cisse wore a Virgin jersey but not the Wonga one.
Cisse wouldn't be the first Muslim player to refuse to wear a jersey on religious grounds.
Striker Frederic Kanoute took a stand at Spain's Sevilla in 2006 when he opted against wearing a shirt sponsored by gambling firm 888.com.
Eventually, Kanoute did wear the shirt but was excluded from taking part in any promotional activities linked to the sponsorship.
"I think every player will have their own (stance) on this," said Mogra. "There will be players who will not be prepared to do something they believe is against their religious teaching and there might be some who might not be so concerned.
"It's very difficult to say how everyone is going to react."
The Council hasn't been approached by the club or Cisse, Mogra added.
"If they were to make a request or approach, we would either signpost them or be able to give them advice," he said.
The chief executive of the Professional Footballers' Association Gordon Taylor -- who is seeking a resolution to the dispute -- did not respond to CNN's request for an interview.
When asked if other clubs had expressed an interest in Cisse, Diene couldn't "answer that question."
Earlier he insisted that Cisse "loves the fans, the club and the city."
Cisse played a significant role in helping Newcastle to overachieve and finish fifth in the Premier League in 2011/2012, scoring 13 goals in 14 appearances after joining from Freiburg for $13.7 million during the January transfer window.
But he cooled last term, netting eight league goals as he played second fiddle to Demba Ba. Ba was then sold to Chelsea and Newcastle barely avoided relegation.
The Cisse saga has added to an already lively off-season at Newcastle, one of England's best supported clubs with an average league attendance last season of more than 50,000.
In June, the Magpies rehired the outspoken Joe Kinnear, which did not go down well with the club's fans. Formerly a manager, he was brought back as director of soccer.