Health Secretary Alan Johnson faces claims he broke donations rules during Labour's deputy leadership contest.
Alan Johnson's team has denied any wrong-doing
The Sunday Mirror says Mr Johnson's 2007 campaign received £3,334 from a man who wrote a cheque on behalf of his brother, a local Labour Party official.
This was among four donations totalling over £9,000 not registered on time.
Work secretary James Purnell said the donations had been declared in various registers and told the BBC it had "been got a bit out of proportion".
Mr Purnell told BBC One's Sunday AM: "They declared all of these to the Labour Party; they paid the levy that you have to pay on them; they declared them to the House of Commons register; they believed they had declared them as well to the Electoral Commission.
"But there were four which turned out not to be on there, so, for the avoidance of doubt, they re-registered all of those declarations.... I don't think there's been wrong-doing."
As well as facing questions about whether or not he declared donations to the Electoral Commission within 60 days, as legally obliged to do, Mr Johnson also faces claims he accepted a "proxy" donation.
'Checked and registered'
The paper says Waseem Siddiqui was used to channel the gift to Mr Johnson's failed campaign.
A statement from Mr Johnson's deputy leadership campaign team said: "We had no reason to believe the donation came from anyone other than (Mr Siddiqui).
"We checked he was a member of the Labour Party and was on the Electoral Register and we registered the donation with the Labour Party, the register of members' interests and the Electoral Commission."
The allegations come days after Peter Hain quit his cabinet posts over a donations row.
Mr Hain resigned as work and pensions secretary and Wales secretary after the Electoral Commission, which is investigating more than £100,000 of undeclared donations to his deputy Labour leadership campaign, passed his case to police.
The Sunday Mirror points to four donations which were made to Mr Johnson's deputy leadership campaign between April and July last year but were not declared to the Electoral Commission in time.
Donations have to be declared within two months of receipt and it is against the law for someone to donate money on behalf of another person.
The statement from Mr Johnson's campaign team confirmed that the four donations - including the one from Mr Siddiqui - had not appeared on the Electoral Commission's register but insisted the paperwork had been filed on time.
It also said the campaign team had met the commission in early December to discuss why the donations were not listed on its website.
An Electoral Commission spokeswoman said permissibility checks were carried out on all declared donations before they were added to its register and the aim was to complete those checks within 20 days.
The Sunday Mirror claims that Mr Siddiqui, 50, was asked to write the cheque by his brother Ahmed Yar Mohammed, who is treasurer of Croydon Central Labour Party.
Mr Siddiqui told the newspaper he did not know who the health secretary was and that he had joined the Labour Party as a student member in March last year, on the advice of his brother.
He is said to be a Pakistani who has been living in Croydon, Surrey, on a student visa for the past three years.
Shadow business secretary Alan Duncan told Adam Boulton's programme on Sky News that the various claims showed that although Labour had campaigned for such laws, they appeared to believe they only covered other people.
Liberal Democrat frontbencher Norman Baker said: "This is another murky situation which will need to be properly investigated if confidence is to be restored."
Home Office minister Tony McNulty said of the registration of donations "there is some time lag which they'll look into... but if the notion is that somehow some sort of wrongdoing then I think clearly there isn't".