Shahzad has taken 14 wickets in nine ODIs for England
England fast bowlers Ajmal Shahzad and Chris Tremlett will fly home from Australia on Thursday to begin their rehabilitation from injuries.
Shahzad tore a hamstring in Sunday's 51-run defeat in Brisbane and was ruled out of the last two one-day matches.
Tremlett, who is not in the 15-man World Cup squad, missed the Brisbane match with a minor side strain.
Paul Collingwood suffered a back spasm in the penultimate match in Sydney but it is not thought a serious injury.
England have two World Cup warm-up games before they face Netherlands in their opening match of the tournament on 22 February.
Shahzad and Tremlett were due to stay in Australia but the England & Wales Cricket Board made the decision to fly the pair home earlier than originally planned to give them more time to be treated in England.
Shahzad's fitness is the priority for the World Cup but Tremlett was expected to provide cover for England's other injured bowlers.
Spinner Greame Swann and seamer Tim Bresnan were forced to return to England with back and calf injuries respectively, while Stuart Broad bowled in the Sydney Cricket Ground nets on Monday as he continues to recover from the
stomach injury he sustained during the second Ashes Test.
England have already called up
Liam Plunkett as cover
for the one-day series.
The Durham paceman was not selected on Wednesday as
Australia won by two wickets
to take a 5-1 lead with one match remaining.