Councils in England have just three years to use any profit made from Right to Buy sales before it is handed over to UK government.
The money can only be used on housing, and can fund up to 30% of any new development, the rest of which has to be funded elsewhere.
The council, which has a 12,000-plus waiting list, has so far managed to plough all £45m of its receipts back into its huge estate regeneration, building 3,000 homes, but is now running out of ways to spend it before the three-year cut off.
Mayor Phil Glanville told the Hackney Gazette: “We’re always looking at new and innovative ways of delivering more affordable housing in the borough. Housing associations are suffering too.
“Homes are badly needed. We’ve sold around 200 through Right to Buy each year since 2012 and though the model is one-for-one, all the restrictions on funding to replace them are hard to meet.
“We’ve seen the receipts return to government in other boroughs and that’s the last thing we want to do.”
Hackney sold 213 of its homes through Right to Buy in 2015/16 and from April 2016 to January this year sold another 120.
Glanville said he was “really keen” to see the money from the Mayor’s Housing Challenge used solely for social homes or “genuinely affordable housing”.
Regarding where they could be built, he said: “We are very clear we don’t want to build on green space. We are consulting on building on car parks, garages and depots and it’s proved quite popular.”
Hackney is the 11th most deprived borough in the country, but gentrification means it also has some of the highest house prices.