The additional funding was due to be approved by Transport for London's (TfL) finance and policy committee but Khan intervened to postpone the decision to allow City Hall to review the financial position.
Temple underground station is undergoing improvement and strengthening works to allow the north end of the bridge to be built on top of it. The extra funding is to be used towards these works. According to the BBC, the Garden Bridge Trust will repay this additional finance and a repayment schedule had been agreed as part of a costs agreement with TfL; with the first repayment being made in June.
The National Audit Office also recently announced it would be reviewing another part of the public funding for the project and the Charity Commission is analysing the Garden Bridge Trusts' spending.
Khan supports the construction of the bridge as long as no more public funding is allocated to the construction and there is more accessibility and transparency. It is estimated the bridge will cost a total of £175m and to date, £60m of public money has been provided to help fund the project.
A spokesman for Khan said: "The previous mayor first approved plans for enabling works to prepare Temple tube station for the arrival of the garden bridge two years ago in the summer of 2014... This enabling work has since been suspended and that will be reported to the finance and policy committee."
"Sadiq Khan has been clear that no new public funds should be committed to the garden bridge and he has pledged to make the project more open and transparent – standards that were not always met under previous administration," said the spokesman.
Planning expert Victoria Lindsay of Pinsent Masons, the law firm behind Out-Law.com, said: "The Garden Bridge proposals have been met with yet further controversy. Whilst Khan officially supports the Garden Bridge, his support is conditional on openness and transparency and no further public funding."
"His recent decision to halt the Garden Bridge works illustrates how less sympathetic he is to the proposals than his predecessor Boris Johnson. However, back in May, Khan said that so much money had already been spent on the build that it would cost more to cancel the project than to build it," said Lindsay.