The 22-year-old, who has been missing from the girls' recent promotional schedule and rehearsals, is currently off work under doctors' orders.
A spokesperson added: "She will be back with The Saturdays soon, when she is fully recovered."
Sandford wrote on Twitter last week: "Sorry I haven't tweeted in a while.I've not been very well.Miss u @MollieTheSats @unahealy @vanessawhite @RochelleTheSats I'll b back soon x (sic.)"
The star's disappearance from the group caused the media and online forums to speculate on the stability of the band and whether Sandford had quit.
Rochelle Wiseman said: "No, we're not splitting. She's not very well and you can't even have a flu or a runny nose before people start saying you've left [the group]."
Mollie King added: "The thing is, as soon as you've been around for a certain amount of time those rumours are always going to start."
Una Healy concluded: "In any other job if somebody had a few days when they were sick, nobody would say they've left. What are you supposed to do? You can't come to work if you're ill."
The Saturdays will release their new single 'My Heart Takes Over' on November 13, while their upcoming album On Your Radar will follow a week later on November 21.
> The Saturdays unveil new album 'On Your Radar' artwork
Watch the music video for 'My Heart Takes Over' below: