The right back has an option to make his move permanent if Fulham trigger a £1.3 million release clause written into his current deal but the 29 year-old suggests it won't quite be as simple as that.
"Nothing is decided yet," the German said, speaking to Kicker magazine.
"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."
Many would still expect Riether to return to Fulham, however, after a hugely impressive first season in the Premier League. He has proved himself to be one of the best full backs around, fusing a healthy resilience with some purposeful wing play. He is, quite simply, everything you'd want from a right back.
As such, Fulham fans have taken to him quickly and Riether is appreciative.
"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."
The one worry there is for Martin Jol is the potential for Riether to make a more lucrative move. Having made such an impact, many other Premier League teams are likely to chase his signature and despite the agreement Fulham have with FC. Cologne, they are not obliged to only take our offer.
And Riether himself admits he's enjoying life in England, even if some parts of it are challenging, such as learning the language.
"It wasn't easy. At first, I got nothing of what our Scottish assistant coach [Billy McKinlay]."