By Martyn Herman
LONDON (Reuters) - Novak Djokovic hopes the spark he has been lacking so far this year will return as he pulls on his Serbia shirt for this weekend's Davis Cup quarter-final against Spain in Belgrade.
The former world number one's appearance in his home city is one of several intriguing plots as the team competition reaches the business end with four hard-to-call ties.
Nick Kyrgios will be leading Australia's charge when Lleyton Hewitt's side host the U.S. in a clash of Davis Cup heavyweights, Belgium take on Italy while Britain, without the injured world number one Andy Murray, are away in France.
Since opening the year by winning the Doha title, world number two Djokovic has managed only six victories, and his ATP Race points total of 475 looks tiny compared with the 4,045 already amassed by a resurgent Roger Federer.
An early defeat by 117th-ranked Denis Istomin at the Australian Open was followed by two defeats by Kyrgios in Acapulco and Indian Wells. He then withdrew before the start of last week's Miami Open citing an elbow injury.
That is why all eyes will be on the 12 times grand slam champion on the indoor hardcourt in the Serbian capital.
"I personally always draw very positive energy from these weeks," said Djokovic, whose career went into warp drive after helping Serbia win the 2010 Davis Cup title.
"These weeks always bring the best out of me."
Spain will offer a formidable test even without world number five Rafael Nadal. World number 19 Pablo Carreno Busta has been one of the form players on the ATP Tour this year and will be supported by 24th-ranked Albert Ramos-Vinolas.
The weekend will kick off in Brisbane where the two most successful nations in Davis Cup history clash for a 47th time.
Australia are seeking a semi-final spot for only the second time in 11 years and much will depend on the form of Kyrgios.
With the U.S. boasting a team of in-form Jack Sock, John Isner, Sam Querrey and Steve Johnson, Hewitt will be banking on two wins from the mercurial Kyrgios as his second singles player is the inexperienced world number 79 Jordan Thompson.
"We've got a big tie against USA. Obviously Jack is playing unbelievable. John (Isner), he's a proven player. They've got a great team," Kyrgios, who lost a thrilling Miami semi-final against Federer last week, told the Davis Cup website.
Britain face a tough assignment without Murray on the clay in Rouen where Kyle Edmund and Dan Evans will be trying to fill his sizeable shoes against a host nation missing Jo-Wilfried Tsonga but led by 17th-ranked Lucas Pouille.
Belgium, the only won of the quarter-finalists never to have lifted the trophy stunned Germany in Frankfurt without David Goffin in round one but will have their top player back for the home clash with Italy in Charleroi.
(Reporting by Martyn Herman)