The 29-year-old has been an ever-present at right back in the Premier League this campaign.
"I can't say where I will play next season," Riether said. "But we will speak in the next few weeks, then there will be a decision.
"It will be the decision of the club and Cologne. They will speak together and in the end they will speak to me.
"But I like to play in the Premier League and it's a great club with great fans. I'm proud to be here."