Lleyton Hewitt prides himself on his preparation but he didn't plan to play for Australia in the Davis Cup tie against the U.S. at Kooyong in Melbourne.
Hewitt, 35, retired after the Australian Open in January and started organising the team for his first tie as Davis Cup captain.
But when a bed-ridden Nick Kyrgios was ruled out of the World Group first-round tie with a severe virus, Hewitt stepped in to replace him in the four-man team.
"Zero," Hewitt replied in January when asked about the likelihood of him playing at Kooyong after his retirement.
But he upped his training once he knew that Kyrgios had fallen ill last week in Dubai.
"Obviously with Nick, when we knew he had some issues, I tried to prepare as well as possible just to be another option," Hewitt said.
"I've been around enough Davis Cup ties now to know you've got to have back-ups and plans in place.
"I'm hitting the ball well and we've got as good a team as we can field going in and I'm confident we can still win."
The former world No.1 so far hasn't nominated himself to play, elevating Sam Groth to the singles in place of Kyrgios as well as doubles with John Peers.
Groth will open play on the temporary grass court against U.S. No.1 John Isner on Friday before Bernard Tomic takes on Jack Sock.
But Hewitt could still inject himself into the doubles rubber - with Groth or Peers - or the reverse singles on Sunday.
Hewitt, Australia's most successful Davis Cup player of all time, said he would do what was best for the team, pending the results and length of matches.
Kyrgios practised briefly on Wednesday in a bid to prove himself fit to play but Hewitt said he had little choice but to put a red line through the world No. 27 who won his first ATP title, in Marseille, in February.
"We took [Kyrgios] through his paces this morning and gave him a little fitness test to see how he pulled up from yesterday but he just wasn't fit enough to play this weekend," Hewitt said.
"It's bad timing for us but it was really out of our hands at the end."
US team captain Jim Courier said he wasn't surprised by the Australian team change.
"We've seen how much Lleyton was practising this week and with Nick's pretty conspicuous absence, but it's certainly not something coming down here that we were anticipating," Courier said.
World No. 20 Tomic has lost his two meetings with No. 23 Sock but he feels confident after reaching the ATP Tour final in Mexico last week.
"I'm playing very well and I'm playing on a surface that's in my favourite," Tomic said.
"I love this grass; it's not too quick and I move well on it so it suits my tennis and it's going to suit Grothy as well so it favours us."