Swann joins all-rounder Tim Bresnan, who has already left Australia with a calf strain.
Adelaide: England spinner Graeme Swann will return to England from the Australian tour because of a back injury.
"He's unfortunately got a strain in his lower back and that, allied with his knee problem, means that it is best for him to go home and get ready for the World Cup now," England coach Andy Flower said on Tuesday. "It is a big blow, he's an important part of our side..."
Swann joins allrounder Tim Bresnan, who has already left Australia with a calf strain. Flower said he was confident Swann and Bresnan would be fit for the World Cup starting in mid-February in India, Sri Lanka and Bangladesh.
Fast bowler Stuart Broad has rejoined the English camp after suffering an abdominal strain in the second Ashes test, but was unlikely to feature in the remaining four games of the one-day series against Australia, which continues on Wednesday in Adelaide.
Australia leads the seven-match series 3-0.
"It is good to have him out here with the squad again," Flower said of Broad. "He is going to be an integral part of our World Cup campaign and having him out here, training with us, and working with out sports science people is where he should be."
Swing bowler Jimmy Anderson, who also rejoined the squad this week after returning home after the Ashes series, will press for selection for Wednesday's match.
Batsman Kevin Pietersen, who missed Sunday's one-day loss to Australia with a groin injury, will be fit to play Wednesday, Flower said.