Confirming the news to the Colchester Evening Gazette, Wilnis said: "It's a real pity. Feyenoord were the team I supported as a boy so I've got a strong sentimental connection with them.
"It would also have been great to have a top Dutch side in action at Portman Road. But I'm still positive and myself and my testimonial committee are very close to getting a top Premier League side instead.
"If it comes off, it'll be very exciting and should hopefully appeal to a lot of people."
You can find more information on Fabian's testimonial year and game at http://www.fab10.co.uk.