The 29-year-old German has been on a season-long loan at Craven Cottage from German club Cologne - who play in the second tier of the Bundesliga.
Fulham manager Martin Jol recently indicated he would be keen to keep Riether in west London, and may trigger a clause to make the move permanent for around £1.3m.
Riether also has a say on whether he would like to remain by the Thames, having featured in 29 games for the club this season.
He told German magazine Kicker: "Nothing is decided yet. Fulham can activate a clause, and I also have to agree.
"As things stand now, I will return to Cologne in the summer. But I have to consider and talk to both clubs.
"I wanted to become a starter at Fulham, and I managed to do that. I am proud I have become a fans' favourite.
"But of course I can still do better, and that's what I am trying to do."
He added that the hardest part of playing in England was to learn the language: "It wasn't easy. At first, I got nothing of what our Scottish assistant coach (Billy McKinlay)."
Regarding the clause when the loan deal expires in May, Jol said recently: "We've got an option on him and I think we will take it. He will probably stay here."
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