The work along Keira Street has had a substantial impact on The Living Room restaurant, according to owner George Antoniou.
On Wednesday night he had 10 bookings on a night when he would normally expect 30 - plus walk-ins.
On Wednesday afternoon the number was so low he wondered if it made more sense to close for the night.
"We've tried to embrace everything that's going on, but it's hard when customer numbers are down due to noise and dust," Mr Antoniou said.
"The numbers have dropped quite significantly, and we knew there would be a drop - but that doesn't pay the bills at the end of the day."
Mr Antoniou said business actually picked up when Keira Street was partially closed because it meant pedestrians had easier access to his cafe.
But that had changed when the gates and fences were relocated to direct people down the centre of the roadway and finding a way through to The Living Room became difficult.
Mr Antoniou said GPT had been "straightforward and upfront" about what was going on, which helped him plan around the works.
When the work finishes in September, Mr Antoniou is hoping to see customers return to his restaurant.
"I hope we get a boost of numbers. That's why we're going through this short-term pain, to get some long-term benefit."
Nam Huynh, partner at Mylan Restaurant, was concerned about limited parking, which affected her takeaway sales.
She claimed Wollongong City Council told her that parking spaces in Market Street could be used by customers but these had since been reserved for construction workers.
Also, once the GPT shopping centre is opened, she was not sure her business would benefit.
"I definitely think more people will come but not more customers for each shop because they will have a lot of shops in there," Ms Huynh said.
"For Wollongong it will be better but maybe not for these businesses."