The Holland international knows his time in England is coming to an end.
"I have a contract for a year after this," Janmaat told Ziggo Sport.
"They always have to pay something, and if Feyenoord cannot do anything, it's okay to talk about it - if I go to Feyenoord, I have to give up some money, which makes sense if you go to the Netherlands from the Premier League, you'll earn less.
"I would always like to return to Feyenoord, which I have always said.
"But it is also difficult, but I would like to, even if I am still at an age that I am fit and can do good things, I do not want to reduce that."