"The first rule in any battle is to never underestimate your foe.
"Which is why I have to spend a lot of time working hard and speaking with the voters and the machinery is also doing so," said the PKR president-elect.
Anwar was in Kuala Terengganu to meet with party members.
The Port Dickson by-election was called after its MP, Datuk Danyal Balagopal Abdullah, vacated it on Sept 12.
Nomination day is scheduled for Sept 29 but there may be a multi-cornered fight.
So far, only Chan, an Internet celebrity better known by his Twitter handle @tapaimalaya, has announced he will contest the seat as an independent candidate.
Parti Rakyat Malaysia has also expressed its interest in running for the seat but has yet to decide on a candidate.
Meanwhile, Umno has decided to boycott the election.
Its long-time rival, PAS, which has been closely cooperating with Umno recently, has also yet to announce if it will toss its hat into the ring.