Lord Foster last week brushed off a £1 million loss on the Millennium Bridge, which closed for an indefinite period this week after heavy pedestrian traffic caused the bridge to twist, throwing its users off balance.
Speaking before the bridge's trouble-hit opening last weekend, Lord Foster described the bridge as part of his charitable 'legacy' to London.
He said that the design team of Foster & Partners and engineer Ove Arup & Partners has lost more than £1 million on the £18 million project.
Lord Foster said that they have donated design time and resources to the scheme which will not be met by fees.
'We quickly had to tear up any idea of making a profit on the project, 'Lord Foster said.
'We were tackling problems which had never really existed before on bridges such as landing on steps, and you have to invent something to solve the problem.
'We do a lot of work on a charitable basis and this was a conscious attempt to put something back into the city where we live.'
Meanwhile, the £18.2 million bridge was closed by police on its opening day on Saturday as people grabbed handrails for stability.
That closure was temporary, but now massive shock absorbers are likely to be fitted on the south side of the bridge to limit the vibrations which are causing the twisting. The bridge was stable during quiet periods over the weekend, but with 200,000 crossing during the course of the weekend, it was tested to its limits.
Engineers from Ove Arup & Partners worked all weekend on the problem, which centred on the Bankside end where the bridge was least stable, and the bridge was closed again on Monday.
At its media opening last week the bridge was swaying lightly and Foster partner Ken Shuttleworth said: 'It's going to move more than this - it's supposed to be quite bouncy.'
Another partner, David Nelson, said: 'It's been a surprise and we weren't expecting it to do that.
But as architects there is not a lot we can do until we see the results of the engineer's tests.'
As the latest closure of the bridge was announced, Lord Foster distanced himself from the problem and stressed that it would be inappropriate to comment because Arup is the lead consultant on the project.
Lord Foster has estimated that more than four million people will cross the bridge each year, which would mean an average of 11,000 people crossing each day, one tenth of the number which crossed on Saturday.