Last year's final, won 18-15 by Selby against his compatriot Shaun Murphy, was held in front of a full house as part of the British Government's pilot scheme for the return of spectators to sports venues, but COVID-19 enforced crowd restrictions were in place for the 2020 edition and the majority of last year's tournament.

Selby won the title for the fourth time last year, and is the top seed at the Championship.

In January, he opened up about the impact of mental health struggles, and prior to this tournament admitted that snooker seems "irrelevant right now."

"Snooker goals seem irrelevant right now, even though this is the World Championship," Selby said, as reported by Eurosport.

"I have had no motivation and it is hard to explain it other than to people who have had [depression].

"The temptation is to say 'just snap out of it', but I just never know how I am going to feel.

"I can wake up and feel a little better, then as the day goes on and I have a cloudy patch and feel much worse.

"It feels like I am fighting myself every day, but I have got great support around me with [Selby's wife] Vikki [Layton] and the family, and now this doctor.

"I will be going to the Crucible probably with a different perspective and hopefully feeling better."

Selby was the last player who clinched back-to-back titles at the Crucible, triumphing in 2016 and 2017, and faces Wales' Jamie Jones in the first round.

In the other half of the draw, world number one Ronnie O'Sullivan faces a tough-looking opener against fellow Englishman David Gilbert, a 2019 World Championship semi-finalist.

O'Sullivan beat first-time finalist Kyren Wilson, also of England, to be crowned world champion for a sixth time in 2020.

He needs one more to match the seven titles won at the Crucible by Scotland's Stephen Hendry.

Australia's world number three Neil Robertson enters the World Championship in fine form, having won his sixth Triple Crown event at the Masters in January, beating England's Barry Hawkins 10-4 in the final.

Robertson also edged past four-time world champion John Higgins of Scotland 10-9 to win the Tour Championship earlier this month.

However, his only triumph at the World Championship came in 2010, and he has not reached the one-table set-up since 2014, having fallen at the quarter-final stage in the last three years.

Crucible debutant Ashley Hugill of England awaits him in the first round.

England's Judd Trump was the 2019 winner, but the world number four has had a mixed season going into an opener against Hossein Vafaei.

Vafaei is the first Iranian player to qualify for the World Championship, and takes the total number of nations who have competed at the Crucible up to 20.

A total of 32 players are set to compete in the first round, with matches held over the best of 19 frames.

Second round and quarter-final matches are due to be held in a best of 25 frames format, followed by a best of 33 for the semi-finals on the one-table set-up.

The final, over the best of 35 frames is scheduled for May 1 and 2.

The winner stands to earn £500,000 ($650,000/€600,000) from the total prize pot of £2.395 million ($3.129 million/€2.894 million).