Fulham's recent £2.5million acquisition was entitled to the fee as part of a sell-on clause in the deal which took him from Watford to QPR in 2004.
The 25-year-old winger said: "Rangers are struggling for money and as everyone knows, I'm a boyhood fan. The club were saying that not enough money had been paid for me. I said: 'I'll give you 10 per cent of the sale'. 'It was my decision - there was no pressure from anyone. The transfer was agreed but I don't want to see them hard up."