The Old Trafford manager is set to accept in writing that he concealed from the Spanish Treasury the income from image rights accumulated between 2011 and 2012, Spanish daily El Mundo has claimed.
Prosecutors have accused him of a £2.9million (€3.3m) tax fraud, the newspaper said.
Mr Mourinho received the concealed income through a company located in the British Virgin Islands, called Koper Services, SA, El Mundo wrote.
The Prosecutor’s Office and State Lawyers will inform the Madrid’s Court of Instruction number 4 of Pozuelo de Alarcón, which led the probe, that the 55-year-old has pleaded guilty, closing the case with a compliance agreement.
The Spanish daily, which has had access to the final details of the agreement, said that the former Real Madrid manager is to receive a six-month sentence of prison for each of the two crimes he was being accused of.
According to Spanish laws, first-time offenders don’t normally serve jail sentences of two years or less.
This means that Mr Mourinho’s one-year jail term is likely to be suspended.
And he also agreed on paying a fine amounting to the 60 percent of the total sum he defrauded the Treasury in two years.
Mr Mourinho will admit to having managed to “render opaque the benefits derived from his image rights” and of giving data to society “that does not correspond to reality”, with the sole purpose of defrauding taxes, El Mundo said.
An analysis conducted by Spain’s Tax Agency has found that Mr Mourinho failed to pay to the Treasury almost £1.5million (€1,611,537.61) in 2011 and more than £1.5million (€1,693,133.05) in 2012.
The Treasury started looking into Mr Mourinho’s finances in 2014.
But they closed his file without finding any crime evidence after he agreed to pay £3.97 (€4.4m) for fee defrauded, penalty and interest through administrative channels.
The state’s body later reopened the case following an investigation launched after Football Leaks, the football counterpart of WikiLeaks, published in 2015 a series of documents argued Mr Mourinho allegedly moved large sums in a tax haven.
The tax fraud scandal also swept over Juventus star Cristiano Ronaldo.
Football agency Gestifute, which represents both football personalities, said in a statement at the time: “Both Cristiano Ronaldo and Jose Mourinho are fully compliant with their tax obligations with the Spanish and British tax authorities.
“Any insinuation or accusation made to Cristiano Ronaldo or Jose Mourinho over the commission of a tax offence will be reported to the legal authorities and prosecuted.”
Mr Mourinho had then chosen to appeal judicially the reopening of his tax file.
(Additional reporting by Maria Ortega and Gerard Couzens)