To retain his Olympic crown, Schooling must fend off these challengers

After last year's Rio Olympics, Joseph Schooling said he was looking forward to forming a rivalry with South African Chad le Clos leading up to Tokyo 2020.

However, some new names have popped up at the Fina World Championships and they could also threaten the Singaporean's defence of his 100m fly crown in Tokyo.

1) CAELEB DRESSEL

Could he have broken Michael Phelps' 100m butterfly world record of 49.82sec, had he not competed in the 50m freestyle final before the 100m fly finale?

There will surely be some debate on this, but there is absolutely no question that the 20-year-old American has emerged from the Worlds as the "next Michael Phelps".

His winning time of 49.86sec in the 100m fly is just shy of Phelps' record, and he is the first swimmer to win three gold medals on a single night at the Worlds or the Olympics - a feat not even Phelps had achieved.

Dressel has been known to excel in freestyle sprints at the short-course yards level, and there had been doubts if he could cut it in the long-course metre meets, such as the Worlds.

Schooling's former Bolles School teammate obliterated those doubts in Hungary with six gold medals (at press time), with a potential seventh on the last day of the meet.

2) KRISTOF MILAK

The Hungarian teen broke the world junior record for the third time at the Worlds when he clocked 50.62sec to finish second in the 100m fly final, behind Dressel.

His timing in the final placed him eighth in the all-time fastest list in the event, and he is only 17.

At 17, Schooling's national record in the event was 53.18sec going into the 2012 Olympics, while Phelps' best at that age was 51.84sec.

3) LI ZHUHAO

The Chinese swimmer is the former world junior record holder in the 100m fly and finished sixth in the final in Budapest with 50.96sec.

Just 18, he has already competed in an Olympic final - he finished fifth in the 100m fly in Rio last year with 51.26sec - and won a silver at the 2014 Asian Games, behind Schooling.

Li looks set to be Schooling's main threat at next year's Asiad in Indonesia.

4) CHAD LE CLOS

The South African, 25, may have bombed out at the semi-finals, but one cannot rule him out at the 2020 Olympics.

He was not favoured to win the 200m fly in Budapest, after Japan's Daiya Seto and home favourite Laszlo Cseh had set the pace in the heats and semis.

But the 2012 Olympic 200m fly champion pipped the duo in the final with his winning time of 1min 53.33sec.