Douglas Ross failed to register his MSP income and earnings from some of his football referee appearances in the official register of income at Westminster.
According to his Commons register, the Moray MP left out his salary earned at the Scottish Parliament where he represents the Highlands and Islands.
Mr Ross donates that wage to charity.
His Holyrood pay is reduced to around £20,000 from the normal wage of more than £60,000 because of his dual role in two parliaments.
He declared £5106.70 from working as an assistant referee since the 2019 general.
But according to a probe published in the Herald, he missed out a further £6,728.57 for 16 matches including the Scottish Cup semi-final between Aberdeen and Celtic.
The payments were made between November 2020 and January this year.
He has not refereed any matches since then.
Mr Ross said it was a genuine mistake and has referred himself to the standards commissioner.
‘Tory sleaze scandal’
The SNP said he is “knee-deep in the Tory sleaze scandal”.
The party also criticised him for missing votes because of his other jobs.
Mr Ross said: “This was an error on my behalf that shouldn’t have happened, and I apologise for not registering these payments on time.
“Since realising my mistake last week, I contacted the Office of the Register of Interests and made them aware of the situation.
“All payments have now been declared, including those from my MSP salary that are donated to charities.”
The bigger concern is that Mr Ross isn’t doing the day job.”
Kirsten Oswald MP
He is also referred to the Standards Commissioner.
The SNP said he is “knee-deep in the Tory sleaze scandal”.
SNP Westminster Deputy Leader Kirsten Oswald MP said: “Triple-jobbing Douglas Ross is knee-deep in the Tory sleaze scandal. The rule-breaking Scottish Tory leader must shift his attention from maximising his outside earnings – and start focusing on his role as an MSP, which is supposed to be a full-time job.
“Failing to declare thousands of pounds from multiple side hustles is a clear breach of the rules – but the bigger concern is that Mr Ross isn’t doing the day job.
“He’s missed crucial votes, including on Tory universal credit cuts, to rake in extra cash running the line at football matches.”
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