Heerenveen are happy with how their cooperation agreement with Bolton is working and hope it will lead to a stronger bond in the future.
The two clubs made contact following a friendly last year and they agreed to work together on a number of issues relating to player fitness.
Heerenveen chairman Koos Formsma claims the agreement is working well and admits it could lead to a stronger association in the future.
"We exchange ideas on the medical sector," said Formsma. "The information is evaluated and we think about how best to prevent injuries.
"It's a low-profile thing, but it appears to be of value and it may lead to an expansion into other areas."
Heerenveen midfielder Ugur Yildirim has confirmed he is no longer interested in representing Holland.
Yildirim came close to playing for the Dutch in 2006, but he has since slipped down the pecking order and is now planning to earn international recognition with Turkey.