Riether, 29, is currently on loan from German club Cologne but has impressed for Fulham since joining in the summer.
The former Wolfsburg full-back has already featured 29 times for Martin Jol's side, but could still be plying his trade back in Germany next campaign.
"Nothing is decided yet," he told German magazine Kicker. "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."
Riether was also full of praise for his fellow Barclays Premier League players and believes the style of football in England compliments his own abilities more than in his native country.
"The players here all have an amazing individual quality," he said.
"Even smaller clubs take on high-profile players for a lot of money - there are also fewer dives here.
"The football here suits me. Moreover, the club is very friendly and I received a warm welcome."