A spectator watching the Olympic rowing received treatment in hospital for a hip injury after she fell from an unstable seat.
The woman fell in the grandstand at the site at Eton Dorney on Saturday, a spokeswoman for Games organiser Locog said.
It comes as other visitors to the Olympics have complained that their seats had collapsed at the venue, at Lord's - where the archery is taking place - and at the Olympic Park.
The spokeswoman said: "A piece of spot welding on a seat in Eton Dorney came loose and unfortunately this resulted in a spectator sitting on the seat losing her balance and sustaining a hip injury.
"Together with the supplier we have checked all the seats they have provided, and a few seats in the venues have been replaced.
"The venues have been inspected and we are confident that the defect has been fixed."
Locog previously said that all 200,000 temporary seats at the Olympics have been checked and less than 100 have been replaced following other complaints.
It said there was a problem with the welding on a couple of seats, which come in a set of four, and there was no collapse.
Another ticketholder also complained of problems with seating at the Riverbank Area in the Olympic Park at Stratford.
Michael Page, from Kent, said he watched hockey there on Sunday.
He told the BBC: "The crowd did a Mexican wave, one row jumped up and the empty seats behind moved forward which meant the flooring collapsed."