The 26-year-old Scotland international was due to see specialists over the knee injury which has sidelined him for the last two games and could mean he will sit out the rest of the campaign.
And Gordon, who has already missed almost six months of the season with an ankle problem, said: "It's automatic to fear the worst. There might be an operation and we will find out whether that is required."
The £9million man added: "It's a possibility that it is the knee cartilage, but I'm trying to remain positive. It's been the worst season of my career for injuries. I have never had anything like this at any stage.
"I have hardly missed a game in my career, so to have two lengthy injuries back to back is disappointing. When you come to a new club in the first couple of years, you want to stamp your authority on things and I have been in and out, which has not been ideal.
"So let's get this season over and done with, stay in the Premier League and look forward to next season to come back stronger."
Gordon's first setback came on the eve of the the derby clash with Newcastle back in October when he suffered the ankle injury which limited him to just two appearances in a run of 26 games as Marton Fulop took over.
But his latest absence just three games into his comeback sparked suggestions he had been dropped after 49 appearances to avoid triggering a £300,000 payment to former club Hearts for playing 50 matches, something chairman Niall Quinn has angrily denied.
He is now unlikely to play a part in the Black Cats' continuing fight for Barclays Premier League survival, although he is well aware of the implications of failure.
Gordon told the Journal: "Staying in the division is huge. For the players, the fans and the club here behind the scenes, there's such a difference in the money side of things if you drop down and that affects what the club will be able to spend. It doesn't bear thinking about what could happen."