Three-time Grand Slam champion Andy Murray is currently 89th in the world rankingsAndy Murray suffered another second-round exit as he was beaten by Jannik Sinner at the Dubai Tennis Championships.
The Briton was bidding for his 700th career victory but lost 7-5 6-2 to the Italian world number 10.
Murray has gone out in the second round at his past four tournaments, dating back to the Australian Open in January.
Elsewhere, Australian Open champion Rafael Nadal made a dominant return in the Mexican Open first round.
Murray claimed a battling first-round victory over Christopher O'Connell on Monday to set up a meeting with Sinner.
The highly rated Sinner claimed the decisive break in a tight first set but was dominant in the second, winning four of the final five games to seal victory.
Murray reached the Sydney International final at the start of the season but has lost his second-round matches at the Australian Open, Rotterdam Open, Qatar Open and now Dubai.
In Acapulco, Nadal beat American Denis Kudla 6-3 6-2 in his first match since claiming a men's record 21st Grand Slam title in Melbourne last month.
The Spaniard is unbeaten in his 11 matches this year.
There were also wins in Acapulco for world number two Daniil Medvedev and British number one Cameron Norrie.
Medvedev, who lost to Nadal in the Australian Open final, beat France's Benoit Paire 6-3 6-4.
The Russian could replace Novak Djokovic at the top of the world rankings depending on their respective results in Acapulco and Dubai.
He will play Spain's Pablo Andujar next, while Nadal faces American Stefan Kozlov.
Britain's Norrie, who won the Delray Beach Open on Sunday, beat Daniel Altmaier of Germany 7-6 (7-5) 6-2 to set up a meeting with John Isner.
