Bernard Tomic's former Davis Cup team-mates have refused to comment on his latest tirade against Australian captain Lleyton Hewitt and Tennis Australia.

On Tuesday, Hewitt said he doubted Tomic would represent his country again after the former world number 17 said Australia could not win without him.

Tomic returned serve, saying he was determined to play for Australia again and prove his doubters wrong, but not before the "whole situation with Tennis Australia" is addressed.

The Australian team left the Tomic issue alone on the eve of the opening tie, with only world-number-five German Alexander Zverev having his say.

"Didn't he say he wanted to be top five by the end of the year when he came out of that jungle camp or whatever you call it? Good luck to him," Zverev said.

One player who has shone in Tomic's absence is 18-year-old rookie Alex De Minaur, who will make his singles debut for Australia on day one of their World Group Davis Cup tie against Germany in Brisbane, starting tomorrow.

The 18-year-old had a breakout summer, making the semi-final of the Brisbane International and the final of the Sydney International.

The Australian team starts its Davis Cup campaign against Germany in Brisbane. ( ABC News: Zane Bojack )

De Minaur will play the first singles match on Pat Rafter Arena tomorrow against the 20-year-old Zverev, with Nick Kyrgios then taking on Jan-Lennard Struff.

"Obviously he (Zverev) is the favourite but I will come out here and put everything on the line," De Minaur said.

"I wasn't expecting any of this, it is a dream come true. It is a great honour representing your country and I can't wait to get out there."

Zverev last year became the youngest top-five player since 2007, and it is expected to be a tough blooding for the rookie Australian.

Sorry, this video has expired Tomic spent last year feeling 'so confused'

"On day one we knew Zverev would be their number one player and we felt that Alex would be able to go out there and test him from the start," Hewitt said.

Zverev admitted De Minaur was an unknown quantity.

"I don't know much because he is a bit younger than me. Obviously we all watched him play this summer, he obviously loves playing on front of the Australian crowd," Zverev said.

"He is in good form but I feel like I am ready."

Despite speculation, Hewitt did not make himself available to play doubles, with Matthew Ebden and John Peers to pair up against German duo Tim Puetz and Peter Gojowczyk.