Speaking at an event on GP commissioning run by the think tank, Professor Chris Ham said management funding must be sufficient for consortia to bring in the people and skills for effective commissioning.
'If it is around £10 per head, will that be enough when you look at how much is being spent to support medical groups and similar examples in other countries?' Professor Ham asked.
He said organisations in parts of the US received £120 per patient to cover management costs, although this was a 'ball-park estimate', and figures were not directly comparable.
Professor Ham listed other factors that should be considered when setting up consortia.
GPs should carefully consider the appropriate size of consortia, he said. 'Scale is necessary when it comes to managing risk. But some of the evidence around total purchasing shows larger groups were often less effective.'
He said choosing which level different services should be commissioned at was key, along with the involvement of secondary care clinicians.
Health minister Lord Howe, also at the event, said GP commissioning would only be effective when a full range of health professionals were involved.
'I hope all GPs will agree that designing and delivering complex services to meet the needs of local people requires effective partnership with other healthcare professionals,' he said.
Lord Howe said the reform process would be challenging and urged PCTs to support GPs. But he added: 'It is for GP practices to come together and form consortia, and it is for consortia to decide how they will organise themselves.
'It is essential it is led by general practice and not by PCTs.'