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The payslip has circulated on a number of fan forums and the Reds are not happy.
It shows the Norway star's home address, national insurance (tax and benefits) number and other personal details.
It also shows the 27-year-old's monthly gross income of £139 634.
"We are taking the matter extremely seriously and we are investigating," a Liverpool spokesman said.
The payslip showed Riise was paid a basic monthly salary of £120 000, received £4 000 pounds in appearance bonuses and a £250 "points bonus".
He was also awarded a Champions League salary increase of £15 384.62.
The left-sided player's tax payment was £55 508.28 and he ended up with £82 413 net after all deductions.
Sixty-five pounds was deducted for meals, £36 for tickets, while there were no contributions in the student loans repayment column, the payslip showed.
Several Liverpool players' homes have been broken into during the last 18 months but Riise's house is not among them.
"It must have been stolen but the player simply doesn't know how it has happened," a club insider said.
"I can assure you that John Arne Riise is not in the habit of throwing payslips out.
"It's clearly been stolen and taken without his permission.
"Nobody would want their details - highly personal details - put all over the Internet."
The local Merseyside Police force said they were not investigating.
In March this year Riise was declared bankrupt by Liverpool County Court for an unpaid debt of around £100 000.
Riise was involved in a legal battle with his former agent, Einar Baardsen, whom he accused of swindling him out of three million pounds.
