O'Sullevan is back in hospital.
In late September, the former 'Voice of Racing', now aged 94, spent more than a week in the hospital being treated for the condition before being released - and days later drove himself to last month's Arc meeting at Longchamp.
O'Sullevan came home from Paris suffering from a touch of bronchitis from which he subsequently recovered, but his mobility issues have since resurfaced.
Keen to allay concerns over his close friend's health, Nigel Payne, who runs O'Sullevan's charitable trust, said: "Sir Peter has returned to hospital. He has leg circulation difficulties and needs to rest.
"He is expected to remain in hospital for a few more days and is in good spirits."
Payne added: "His answering machine at home is full to capacity with goodwill messages."