Education secretary Michael Gove has come under-fire for scrapping the requirement for all pupils to have at least two hours of PE a week, while local networks that organise sporting events are also being dismantled.
Basketball has been one of the hardest hit sports after an announcement last month that the sport will receive zero funding in the run up to the Rio Games in 2016 – having been handed £8.5million for London.
Now Deng, who is one of the star players for the Chicago Bulls, said the actions of the government risk "completely demolishing" the good work done at the London Games.
"We all heard about the 'legacy' that London 2012 was going to bring to sport in the UK and I refuse to sit back and let that legacy be completely demolished for basketball," he said in his letter to Cameron.
"I, along with other people involved in the game, have put too much in and care too greatly to let this happen.
"The sport of basketball is a pathway, a pathway that teaches so many valuable lessons on and off the court, how are we supposed to motivate these kids to carry along their journey when there's now nothing at the end? No Team GB, no Olympic dream, no goal."
Shadow education secretary Stephen Twigg was similarly scathing after the results of a new survey showed that a majority of people think that support for sport has been stagnated or cut since the last election, despite the country's biggest ever sporting festival having taken place last summer.
"Six months on, the Olympic legacy is in tatters," Twigg is quoted as saying in the Daily Telegraph.
"This survey shows those booing George Osborne in the Olympic Stadium spoke for the nation.
"We've seen partnerships that enabled primary school children to do competitive sport scrapped and the proportion of pupils doing two hours of sport a week collapse from 90 per cent under Labour to 50 per cent now.
"Labour would get Ofsted to inspect school sport, enable teaching assistants to become PE teachers, and ensure parents know how much sport their children get at school."
A Government spokesman said: "We are working on a variety of measures to improve school sport as part of the Olympic and Paralympic legacy. We will announce our plans in due course."