The Republic of Ireland international has been sidelined for several weeks by the problem, which requires an operation to correct.
However, a scheduled appointment has had to be cancelled because Westwood has been ill and is taking a course of antibiotics, and the delay means his season could effectively be over.
Sunderland boss Gus Poyet said: "It has been postponed because of a little illness. You cannot have an operation when you are ill, so he is on antibiotics now."
Asked how long the player is likely to be out, the Uruguayan said: "I would like to say three to four months. Now, if you are going to think when is the season going to finish, it's probably to the end, yes."
Meanwhile, Poyet admits Sunderland's January transfer dealings with determine whether they can secure their Premier League status.
The Black Cats are in FA Cup action this weekend but there will be work going on behind the scenes as Poyet bids to strengthen the squad he inherited from Paolo Di Canio.
Asked if the success or otherwise of that mission would determine the destiny of their season, a frank Poyet said: "Yes.
"We have been there already with three different managers or head coaches or caretakers with this group of players, and the team is bottom somehow, so we need a little bit of help. We will see.
"We have been here now this season for five months - I am not talking about me, I am talking about the previous manager, Kevin Ball as the caretaker and me - with this group of players, and we are still bottom, so I want to change something.
"I am not going to go with the same group of players to the end because if not, it's going to be more difficult.
"Now I need to choose well and make sure we get the ones who can really help us to change the season around, that simple."
Sunderland are understood to be in negotiations with Poyet's former club Brighton over midfield duo Liam Bridcutt and Will Buckley, having already completed the loan signing of Fiorentina full-back Marcos Alonso.
However, Poyet is refusing to discuss his targets publicly as agents bombard the club with offers, and he dismissed Celtic and Hull's interest in Steven Fletcher as "speculation".
"They didn't call me and they didn't make any offers, so it is speculation, rumours," he said.
"It's easy. I am interested in (Cristiano) Ronaldo. Apparently he doesn't want to come to Sunderland, it's too cold.
"We can say and talk and make opinions and go on TV and make it look incredible, that we want to buy this and that.
"But do it and then we will talk about it."