MPs have raised "serious concerns" over the appointment of a senior civil servant to oversee Whitehall's recruitment process.
The role has previously gone to people from outside the civil service, the public administration committee said.
There were also "reservations" over Sir David Normington starting the £85,000-a-year job straight after retiring from the Home Office on a pension.
But the committee said it had "every confidence" in him as an individual.
The government has reformed the way Whitehall's recruitment process is overseen, by combining the roles of the First Civil Service Commissioner and the Commissioner for Public Appointments into a single job.
Sir David, who retires as Permanent Secretary at the Home Office at the end of this year, will be paid £85,080 a year for the new three-day-a-week job.
In a report, the committee said the government had not "made its case" for such a change, adding: "We reserve our position about the wisdom of this reform, subject to our own examination of the impact it will have on the two offices."
It added: "While we recognise the constraints on the public purse, we have reservations that Sir David will be able fulfil the two roles as adequately as his predecessors on the basis of the same time commitment for both jobs as his two predecessors gave to each of theirs.
"There is a severe risk that one or both Offices will not receive the requisite amount of attention."
Sir David, currently on £189,000 a year, has been a civil servant since 1973.
The committee noted that the two holders of the commissioners' roles, and their recent predecessors, had been recruited from outside Whitehall.
It said: "There is a view that these roles need to be perceived as independent if they are to enjoy the confidence of civil servants and of the public more widely.
"We are satisfied that Sir David has the professional competence and personal independence for the posts of First Civil Service Commissioner and Commissioner for Public Appointments.
"However, these two posts regulate recruitment into public service and are, respectively, the complaint authorities for breaches of the Civil Service Code and the Code on Public Appointments.
"Therefore, we have reservations about the desirability of moving away from the recent practice of appointing from outside the Civil Service, instead appointing a career civil servant to these posts, who is in this case, moreover, being appointed directly on his retirement."
The combined role, which Sir David is taking up from 1 January next year, will not result in any extra pension payments.
But the committee said it had "reservations about the ability of a civil servant to benefit from a significant public sector pension entitlement immediately before going on to secure another public appointment".
Sir David recently featured in a BBC documentary about the Home Office, by the film-maker Michael Cockerell.
He was permanent secretary at the education department before joining the Home Office in 2005.