There is a 60% global shortfall in funds for malaria control, according to a report by UK and African experts.
Researchers found only 21 out of 93 countries where malaria is common have received enough money to implement effective control measures.
African countries have seen the biggest funding increases but billions are still needed elsewhere, the experts say in the Lancet medical journal.
The Roll Back Malaria Campaign warned $4.9bn (£3.1bn) was needed this year.
The researchers, led by Professor Bob Snow of Oxford University and Kenya's Kenyatta National Hospital, found that annual international funding had increased by 166% - from $730m to $1.94bn - since 2007.
They said: "Any decline in malaria-funding commitments will run the risk of a resurgence of malaria in countries that have enjoyed the benefits of this funding to provide protection from malaria since 2002.
"Sustained funding in these countries is crucial or $9.9bn invested since 2002 will have been in vain."
While financing for malaria control has increased as part of international efforts to reach the Millennium Development Goals, the amount received from domestic sources varies greatly.
Twenty-one countries, 12 of them in Africa, now receive adequate donor money, according to the research.
But a further 50, including Niger and Sierra Leone, as detailed in the Lancet paper, do not get enough from the international community.
Professor Snow said: "Poor countries with inadequate donor assistance and large sectors of their population at risk of malaria must remain the focus of attention if global ambitions for malaria control are to be realised.
"The challenge will now be on finding more money, making sure funding is linked to performance and putting pressure on malaria-endemic countries with large domestic incomes to do more for themselves.
"A failure to maintain the momentum will mean money spent so far will have been for nothing."
The authors also argue that some countries like China and India, which have their own space programmes, could perhaps contribute funds to help other countries rather than being recipients, thereby increasing the financial support available.
But the work only assesses external funding.
Commenting on the study, Professor Anne Mills, from the London School of Hygiene and Tropical Medicine in the UK, said that external funding may be low because a country may be funding its own malaria programmes.