David Walliams is still suffering from the after-effects of his charity Thames swim.
The funnyman struggled with a stomach upset after swallowing bacteria-filled water during the 140-mile (225km) swim, which raised more than £1 million for Sport Relief, and has still not recovered.
A Comic Relief spokeswoman said: "We understand David has contracted a bug that has caused a stomach upset. He is being treated for this and has been advised by medical professionals that it is not serious and that he will soon be back to full health. David has not been tested for Weil's disease."
He also tore a disc in his back as a result of his efforts.
David was greeted by thousands of fans at Westminster Bridge when he finished his gruelling eight-day journey earlier this month.
The 40-year-old had to contend with not only the aches and pains of the swim, but also diarrhoea, vomiting and low energy levels from "Thames tummy".
He also struggled with a painful rash where his wetsuit rubbed his neck after the cold water forced him to abandon plans to swim in trunks.
He burned nearly 66,000 calories as he powered through 107,062 strokes on the 140.54-mile (226.17km) trip.
In 2006 David swam the Channel, raising £1 million in aid of Sport Relief.
He has also swum the Straits of Gibraltar and last year cycled from John O'Groats to Land's End, also for Sport Relief.