Tony Abbott believes his Sydney electorate will be the "most fiercely contested political territory in the country" in the weeks leading up to the federal election.
Independent candidate Zali Steggall is hoping to boot the former prime minister from his northern beaches seat of Warringah.
She would need a hefty 12 per cent swing to do so, but has the support of activist group GetUp.
The group held a national campaign launch in the seat on Thursday, after Prime Minister Scott Morrison confirmed Australians will go to the polls on May 18.
Mr Abbott says he's is taking the location of the event as a back-handed compliment that he is not a "washed-up has-been".
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But he also believes it shows he has a serious fight on his hands.
"This is going to be the most fiercely contested political territory in the country in this upcoming election," he told 2GB radio from the Dee Why RSL on Thursday.
"There's absolutely no doubt that at the moment, I'm the underdog.
"As things stand, I'm going to be way outspent by GetUp, the unions and covert Labor operatives coming into the seat."
Despite the challenge, Mr Abbott said he has no plans to retire until a tunnel connecting the northern beaches to the north shore is finished, a prospect at least five years off.
"There is no way on God's earth I'm ever going to retire until this tunnel is built."
