Pienaar says Fellaini will be smart enough not to depart Goodison at a pivotal point of his career on Merseyside when he is playing better than ever.
He said: "He's enjoying his game at the moment so I don't think he'll want to disturb that progress. He's clever enough not to go.
"I don't think he will go in January. I'm sure the manager will keep hold of him.
"There's a lot of speculation about but he's still contracted to the club, and if we keep going like this we know it might still be hard to keep hold of him in the future - but who knows? He's been very important to us these last few weeks."