Announcing it here today, the England and Wales Cricket Board issued a statement saying the Somerset batsman has suffered a recurrence of the stress related illness which led to him returning home from England's tour of India earlier this year.
''Trescothick flew out of Sydney International Airport earlier on Tuesday and will play no further part in the Ashes Test Series,'' it read.
The England selectors will hold urgent discussions over the next 24 hours about a replacement for Trescothick and an announcement will be made in due course, the ECB statement said.
Disappointed after losing the key batsman, England coach Duncan Fletcher was quoted as saying, ''Following discussions between Marcus and the England medical staff, it was decided that Marcus should fly home at the earliest opportunity.
''We are naturally disappointed to lose a player of his quality from our Ashes squad and everyone in the dressing room hopes that he is able to make a full recovery and resume his cricketing career,'' he added.