The accident occurred around 8.15pm at the site of the Bongarde mall being built at Villeneuve-la-Garenne in the Hauts-de-Seine department, according to a report from Le Parisien.fr.
The size of the slab, which fell from the first floor, was estimated at 100 square metres.
Two other workers were reportedly treated for shock, while a third was slightly injured.
A total of 20 workers were on site when the concrete fell.
The site benefited from a special authorization to allow construction work to proceed until 10pm, Le Parisen said.
The cause of the collapse was not immediately known.
Forty fire fighters arrived on the scene to stabilize the structure.
Located near the A86 autoroute near the Seine River, the Bongarde shopping centre was scheduled to open next year.
According to information on the website of the municipality of Villeneuve-la-Garenne, the mall will be one of the biggest shopping centres in the greater Paris region with 86,000 square metres of floor space.
The main building is 320 metres long and 25 metres high, geared for 100 shops, including the biggest Carrefour hypermarket in the metropolitan area.
The project was launched in 2011 at a cost of 140 million euros.