John Millman is on standby for a Davis Cup call-up as Australian captain Lleyton Hewitt sweats on Nick Kyrgios’s fitness and availability for next week’s World Group playoff with Slovakia.

Hewitt must nominate his team to the ITF on Tuesday and plans to include Kyrgios alongside Bernard Tomic, doubles specialist John Peers and Sam Groth or James Duckworth.

But with Kyrgios in doubt with a hip injury that forced his withdrawal from the US Open in New York, Millman is suddenly in the frame.

“He wasn’t part of it initially purely because we had to look at doubles options as well,” Hewitt told AAP.

“So John Peers, Grothy and Ducks were the original squad.

“But Millman is certainly the next best singles player and so I’ll be speaking with him and working out how Nick’s going and then I’ll have to make a plan on that.

“I’m definitely covering all my bases and giving ourselves the best opportunity.”

After a series of devastating injuries, Millman has rebuilt his career and ranking with a fine 2016 season and was unlucky to draw eighth seed Dominic Thiem in the first round at Flushing Meadows.

Millman lost in five sets and Hewitt is backing the world No.66 to do the job for Australia if asked to make his debut in the grasscourt tie at Sydney Olympic Park from September 16-18.

“I thought he played really well in New York. He would have beaten a lot of players if he didn’t draw a guy like Dominic Thiem,” Hewitt said.

“That was a really high quality match.”

Kyrgios is racing the clock to be fit to spearhead the Australian team.

“Hopefully we’ll have Nick in the team. But if we don’t, we still think we can put out a good outfit there and we want to get back in the World Group,” Hewitt said.

“We’ve just got to focus. We’re not taking the Slovaks lightly whatsoever.

“But we think we can get the job done.”