World No.14 Kyrgios and rookie Alex de Minaur must win their reverse singles rubbers on Sunday for Australia to qualify for April's quarterfinals after Matthew Ebden and John Peers lost the crucial doubles clash in five sets on Saturday.
The visitors sprung a late change, replacing Peter Gojowczyk with Jan-Lennard Struff but it was doubles partner Tim Puetz who proved the difference in the 6-4 6-7 (1-7) 6-2 6-7 (4-7) 6-4 win at Pat Rafter Arena.
Germany team captain Michael Kohlmann revealed he was convinced Kyrgios would play doubles and admitted to breathing easier when the Australian No.1 was officially omitted on Saturday.
While Kyrgios didn't appear in the doubles, Hewitt warned the dual grand slam quarterfinalist was ready to make his presence felt on Sunday.
In what Hewitt predicted would be a five-set clash, the tie will go on the line when Kyrgios takes on world No.5 Alex Zverev in Sunday's opening reverse singles rubber.
If Kyrgios is triumphant, 18-year-old debutant de Minaur will then need to step up and seal the tie against power-serving world No.58 Struff - ranked 81 spots higher than the plucky Australian.
"They are two of the young, talented players on the tour - it's going to be a great match over five sets," Hewitt said of Kyrgios' much anticipated clash with German star Zverev.
"I am glad I have got Nick on my side.
"He has played so well for me in the past - hopefully he can go out there and do it again.
"We are a long way from beaten, that's for sure."
Former world No.1 Hewitt had hinted that he may play on Saturday but resisted the temptation, pairing Ebden with world No.4 doubles specialist Peers.
Kohlmann revealed he expected Kyrgios to be the man injected into the doubles after the Australian No.1 needed barely 90 minutes to brush aside Struff in straight sets in Friday's singles.
"When I heard Australia didn't make a change I had a very good feeling," he said.
"I thought Nick was playing for sure. He played one hour 30 minutes yesterday - I don't even know if he was sweating."
Ebden and Peers looked to have justified Hewitt's selection, showing tremendous fight to come back from two sets to one down and force the Germans to scramble.
But it was 30-year-old journeyman Puetz - in just his second Cup tie - who stood tall, thrashing forehand winner after winner as Germany prevailed in a rubber lasting almost four hours.
Ebden admitted they had been "quietly surprised" by Puetz, a lowly No.144 in the doubles rankings who only made his Cup debut last year.