A clause in the contract of the 27-year-old Senegal striker would allow him to quit St James' Park for £7.5m in the New Year.
Pardew remains hopeful of securing a new contract with Ba but is taking nothing for granted, as several clubs are reportedly showing interest in meeting the terms of his release clause.
Pardew said: "Really and truly this window is the key, I think, because if Demba goes in this window, it will cause us a problem.
"I think he will stay, but there's a possibility he could go because of the clause that's still in force.
"In the summer, I won't let it run until the summer. I'll do something about it. We will either move Demba on or we will secure him in the summer.
"Some of the speculation that runs around him - yesterday he was asked about his home-town club, PSG, would he like to play for them one day, and he said yes, of course.
"That's now a headline that he's going to play for them next week. The media kind of fuel it and I understand that, that's part of their business.
"But for our part, he has always put out for us, he has scored more goals than anyone else for us, he is playing well and that's what I have to focus on."
Ba joined the Magpies on a free transfer from West Ham in the summer of 2011.