The General Medical Council (GMC) said it decided to "defer" the revalidation of more than 5000 doctors.
So-called responsible officers, who conduct the assessments, can recommend that a decision to revalidate doctors is deferred if a medic is subject to local disciplinary proceedings or if the doctor has been unable to gather all the supporting evidence in time.
Since the process began a year ago, the GMC has agreed to defer the requests of 5077 doctors from across the UK, including more than 1000 GPs.
A GMC spokeswoman said that deferral requests give responsible officers more time to make a recommendation about a doctor.
Once a deferral request has been accepted, the responsible officers have a year to make a recommendation.
The GMC said so far 22,000 doctors have been successfully revalidated - meaning they meet the appropriate clinical standards.
Before the revalidation process, doctors could go for their entire careers without facing any formal assessment of their competency. But now they face tests to see if they are fit to stay on the medical register.
The assessment takes the form of an annual appraisal - featuring input from patients - and a more comprehensive meeting every five years.