The defender is currently on loan at Craven Cottage from FC Koln until the end of the current campaign.
"As things stand now, I will return to Koln in the summer," the German told Kicker. "I have to consider and talk to both clubs.
"Nothing is decided yet. Fulham can activate a clause and I also have to agree.
"The football here suits me. Moreover, the club is very friendly and I received a warm welcome."
Riether has made 29 appearances in all competitions for the Cottagers this season.