The report was commissioned in February as the Government is aiming to cut the cost of sickness to the state and employers.
The Government will reportedly be urged to set up a panel to assess whether people are too ill to work, so that employers do not have to rely on family doctors, according to leaked findings, reported in the Financial Times of an official report into long-term sickness.
The report was commissioned in February from David Frost, former head of the British Chambers of Commerce, and Dame Carol Black, the government's director for health and work.
Speaking to Sky News, Black said: "the report was looking at the sickness system in Great Britain and we had to look at the journey from being in work to going out of work and what we concluded really is that the journey is not ever fit for purpose and GPs are never removed from this.
"GPs have told us they do not have adequate occupational health advice and in the short time they have with patients they don't have time to do an in depth functional assessment.
"We believe if we give GPs and employers this independent assessment service they, early in this journey, will be able to refer their patient.
"There will be costs, but they will not be in comparison to rewards they will get from this for every person we save [from long term absence]."
Back added that if an employee is off work for 20 weeks sick, there is only a 5% chance of them returning and that the UK had a £13 billion sickness benefit bill as employers annually pay £9 billion in sick pay.
She said: "We only have to save 5,000 people moving into employment support allowance, to pay for this service."
The leak came as the Department for Work and Pensions published a report of findings from qualitative research with GPs to examine their views on the Statement of Fitness for Work (fit note).
It found the fit note has become a consultation tool that GPs use to initiate and guide negotiations with patients about returning to or commencing work. GPs use the fit note to justify why they have initiated discussion about work and to prompt them through the process of questioning patients about their work-related capabilities.
GPs perceive that the fit note is most effective for patients with conditions such as ME/chronic fatigue syndrome, mild-to-moderate mental health conditions, and musculoskeletal conditions. But they are less confident in using particular options on the fit note, like the amended duties and workplace adaptations tick boxes. Some reported difficulty in understanding and distinguishing between the four return-to-work tick boxes and confusion over date fields.
Barriers to the successful use of the fit note include GPs' confidence in dealing with conflict and their perception that it could damage their relationship with their patients. GPs are also less likely to drive for a return to work if they perceive the patient's job to contribute to their health condition.
And many GPs believe that motivating their patients to return to work is an integral part of their role and that the fit note has helped them to do this. It has also helped some GPs to adopt a stricter role with their patients.