Gregson, who plays Rovers Return boss Steve McDonald, was sent home by the show's doctor yesterday morning, The Mirror reports. He later joked to reporters outside his home that he was suffering from "man-flu" and showed a prescription for antibiotics.
Charles - Lloyd Mullaney on the programme - was also absent from set yesterday after his wife called in at 7.30am to explain that he had been unwell all weekend and could not attend work.
A show spokesperson confirmed that bosses had been forced to do "a bit of juggling" due to cast absences.
Coronation Street cast and crew are currently filming crucial Christmas scenes. However, backstage disruption began earlier this month when Michael Le Vell, who plays Kevin Webster, took time off while he fights to clear his name following a sexual assault allegation.
Le Vell strenuously denies the accusation and is expected to return to work on Thursday.
> Read more Coronation Street news and spoilers