West Ham United co-owner David Sullivan has revealed that the club still owe Sheffield United in excess of £10m over the illegal registration of Carlos Tevez and Javier Mascherano.

The Hammers, who controversially avoided a points deduction, were initially fined £5.5m by the Premier League in 2007 for acting improperly and withholding vital documentation over the ownership of the Argentina internationals.

However, following their final-day relegation to the Championship later that year, the Blades opened legal proceedings against the Upton Park club and the two sides eventually agreed a £26.5m out-of-court settlement in March 2009.

Sullivan says that the implications of the agreement significantly restricted his club's options in the transfer market this summer.

"We've done some good business and brought in some real quality despite our still-limited resources," he said.

"We have an eight-figure sum still outstanding over the Tevez affair, even though we have been paying it down over the past two years.

"That amount has to be paid off over the next 12 months, which does take its toll on our transfer activity."

Sheffield United are currently competing in the third tier of English football for the second consecutive season.