With the withdrawal of Roger Federer, Grigor Dimitrov will be thrust into the favourite's role when the Dubai Championships start on Monday.
The Bulgarian is ranked No. 4 in the world and won the season-ending ATP Finals in November, but he lost to Federer in the Rotterdam final a week ago, at the end of a tournament in which the 36-year-old Swiss regained the No. 1 ranking.
Tournament officials waited hopefully all week for Federer, but he finally decided to skip the event.
He informed organisers that he would head to the US next week to begin preparation for title defences at the Masters 1000 events in Indian Wells and Miami.
The 20-time Grand Slam winner did offer to make himself available for Dubai in 2019.
"I believe whatever's good for him is good for us. You can’t really push him more," said Dubai tournament director Salah Tahlak.
"Had he not won in Rotterdam he would have definitely come here. I really respect him, as a professional and as an athlete.
"He's so classy and has done well for the game, has done well for Dubai. He's a legend."
Dimitrov takes over the top seeding at the Aviation Club. Frenchman Lucas Pouille, based in the emirate, is seeded second, ahead of Spain's Roberto Bautista Agut, Damir Dzumhur and Frenchman Richard Gasquet (fifth).
Dimitrov has had a week to heal after playing Rotterdam while ill.
"The good thing in tennis -- there's always the next week," the fourth-ranked Bulgarian said. "You pretty much can play every week that you want. There's always that silver lining."
Dimitrov opens with a tricky test against Tunisian wild card Malek Jaziri, with Pouille facing a qualifier.
North African Jaziri was a quarter-finalist here in 2014 and in 2016 beat two-time finalist Mikhail Youzhny. He also took a set off Federer in the first round in 2013.