Defending Miami Masters champion Andy Murray has not reached a final since having back surgery in September and has dropped to No.6 in the world.

Andy Murray will have to solve the problem of his patchy play quickly if he hopes to defend his Miami ATP Masters title against a star-studded field.

Murray departed Miami last year ranked second in the world after a razor-thin victory over David Ferrer in the final gave him his second Miami Masters title.

He went on to claim an emotional second grand slam title at Wimbledon, but the 26-year-old has yet to reach a final since having back surgery in September and is currently ranked sixth in the world.

The Scot was at a loss to explain a third-set collapse against big-serving Canadian Milos Raonic in the fourth round at Indian Wells last week and admitted his confidence was at low ebb.

That will put him at a distinct disadvantage against the likes of world No.1 Rafael Nadal, who returns to Miami after skipping last year’s tournament to rest his troublesome knees.

World No.2 Novak Djokovic also arrives in Florida brimming with confidence, having secured his first title of 2014 with a triumph over a revitalised Roger Federer in the Indian Wells final on Sunday.

“It was the first final I played this year,” Djokovic noted.

“It was necessary for my confidence and hopefully I can carry that into Miami and the rest of the season.”

Djokovic said Federer was clearly a force to be reckoned with now that he has put his injury-marred 2013 campaign behind him.

“Roger is playing at a very high level,” Djokovic said.

“He has more depth on his shots, especially from the backhand side. He gives himself an opportunity to finish with the forehand. He serves well. He just played better than he did in the last 13, 14 months.”

Women’s world No.1 Serena Williams returns to defend the title she won last year with a victory over Maria Sharapova in the final.

Williams will no doubt be eager to get back on track after her season-opening triumph in Brisbane was followed by a fourth-round loss at the Australian Open and a semi-final loss to France’s Alize Cornet at Dubai in February.

Sharapova will try to bounce back from a third-round loss to Italian qualifier Camila Giorgi at Indian Wells.

The Russian reached her fifth Miami final last year, but has never won the title.

China’s Australian Open champion Li Na arrives in Florida after a semi-final defeat to eventual champion Flavia Pennetta in Indian Wells.