The developer wants to extend the length of its covered 'Eastbrook Mall' walkway, by moving a glazed entrance further out.
The change would not add any more shops but would mean that more of the shopping centre would be under a glass covering.
In its application, Westfield said the change was being sought "to meet the prospective tenant requirements".
A spokesman for Westfield said: "It's a variation on the existing planning approval to move the entrance doors to accommodate a potential new retailer."
But the firm is staying tight-lipped about who the potential new retailer is.
Retailers already signed up to take on units at the £260 million shopping centre include Debenhams, Marks & Spencer, Next, River Island, Top Shop and Top Man, Burger King, KFC and Hey Potato.
The centre is due to open by December 2015.
The latest planning application will be considered by planners over the coming months, once members of the public have had a chance to make any comments.