Novak Djokovic and Andy Murray can set up a Davis Cup quarter-final blockbuster if they successfully pilot Serbia and defending champions Great Britain through the first round.
However, the world’s top two players will go into their home clashes against Kazakhstan and Japan respectively this weekend with question marks over their fitness and match sharpness.
World number one Djokovic saw his streak of 17 successive finals come to an end in Dubai last week when an eye infection forced a quarter-final retirement.
Murray, meanwhile, hasn’t hit a ball in anger since losing to old rival Djokovic in the Australian Open final almost five weeks ago.
The 28-year-old took February off after his wife Kim gave birth to their first child, Sophia.
Djokovic led Serbia to the 2010 Davis Cup title.
“I am optimistic and I hope that I am going to play,” said the 11-time major winner. “I was a little sceptical but now all is going well.”
Djokovic and world number 23 Viktor Troicki will play singles for the Serbs in Belgrade while Kazakhstan’s top player is Mikhail Kukushkin, the world 79.
Murray, who led Great Britain to their first Davis Cup title in 79 years last November, said being a new father has not affected his sleep patterns.
“It was very different to what I expected,” he said. “I still practise hard and do all the same things I was doing before. I will find out if it is different on Friday or not.”
The key clash in Birmingham could come on Sunday when Murray takes on Japan’s top player, Kei Nishikori, the world number six.
Murray holds a 5-1 career advantage over Nishikori ahead of the first Davis Cup clash between the two nations since 1931.
“Britain have one of the best teams with Andy and his brother (doubles star, Jamie). It’s a great challenge,” said Nishikori.
Hewitt plays it again - Should Serbia and Britain emerge victorious, they will clash in the UK from July 15-17 for a place in the semi-finals with Murray already revealing that he intends to play.
In Melbourne, former world number one and two-time major winner Lleyton Hewitt could be drafted into action as a playing captain in the clash with the United States after Nick Kyrgios was ruled out through injury.