Defending champion Chen Long heads into next week's badminton world championships in Indonesia as firm favourite, but faces a challenge from a gutsy Lee Chong Wei who has come back strong after a recent doping ban.

Chen, 26, is in superb form having swept four titles this year and enters the Jakarta tournament a convincing top seed, with Danish star Jan O Jorgensen a distant second.

The world number one won't cross top rivals Lee or Lin Dan in the early stages -- they are in different halves of the draw -- and is expected to cruise to the quarter-finals without incident.

But from there things could get trickier for the Chinese star with a likely clash against seventh-seeded Dane Viktor Axelsen who nearly overpowered him in the Australian Open finals in May.

Chen prevailed in that contest but it hasn't all gone smoothly this season, with a series of shock defeats marring his otherwise impressive run, including at the Indonesian and Singapore Opens.

"It doesn't matter if you are number one or number two. You have to prepare for everything," he told Indian media after his narrow victory over Axelsen in Sydney.

Much attention will be on Malaysia's Lee at the week-long tournament, which starts Monday.

He was runner-up in last year's world championships but was stripped of his silver medal and slapped with an eight-month ban after testing positive for a prohibited substance.

Former world number one Lee's ranking plunged during his stint in the wilderness, but he has gained ground since returning to the circuit in May, winning back-to-back titles at the US and Canada Open.

The 33-year-old will be unseeded for the first time in years at next week's tournament but the shuttler, sporting a new blue hairdo, believes that will work in his favour as he chases his first world title.

"In recent years I've been competing as top seed and the man to beat but now I'm an underdog," Lee told Malaysian media. "This is my year."

Luck on Lee's side

Lee's hopes of winning a world crown were crushed in the last three world championship finals, with long-time foe Lin defeating him twice and Chen dashing his hopes last year.

But Lee might have luck on his side this time. Thanks to a favourable draw, the Malaysian is separated from his arch-rivals in the early stages and won't face Lin until the semi-finals -- if he makes it that far -- and Chen until the final.

Many seeds have opening round byes but Jorgensen must navigate his way past Thai shuttler Boonsak Ponsana at the outset if he's to have any chance of becoming the first European winner since 1997.

Home favourite and 15th seed Tommy Sugiarto has a first-round date with European Games victor Pablo Abian from Spain, while fourth-seed Kento Momota from Japan squares off against Germany's Dieter Domke.

In the women's draw defending champion and world number one Carolina Marin will be looking to cap a tremendous season with her second straight world championship crown.

India's Saina Nehwal only just trails the top-seeded Spaniard, while China's Li Xuerui will be out for revenge after Marin upstaged her in last year's world championship finals in Copenhagen.

There could be history in the mixed doubles if local star Liliyana Natsir wins gold with partner Tontowi Ahmad and claims a record-breaking fourth world championship.

But to get there the Indonesians will have to fend off polished pairs from Hong Kong and South Korea, and a berth in the final would almost certainly mean a showdown with one of the Chinese pairs seeded one and two.