Australia skipper Lleyton Hewitt admits he's not sure what Canada team his Davis Cup side will face in Friday's quarter-final in Madrid.
The Canadians were rocked by an injury to Milos Raonic on the eve of the tournament and lost teenage sensation Felix Auger Aliassime to an ankle issue ahead of their opening match against Italy.
The 19-year-old did not play in either of the Group F matches with Vasek Pospisil and the former junior Wimbledon champion Denis Shapovalov carrying the load against Italy and the USA.
Shapovalov, who beat Australia's Alex de Minaur in the 2016 junior final at the All England, is ranked 15 in the world and defeated Italian world No.8 Matteo Berrettini and Tyler Fritz in his two singles rubbers.
Pospisil saw off Fabio Fogninii and giant-serving America Riley Opelka in his singles matches and the exhausted pair caused controversy by conceding their dead doubles rubber against the Americans - handing them a 6-0 6-0 win.
Mystery surrounds the fitness of Auger-Aliassime and Hewitt admits he is wary of the the 14th-ranked side.
"Pospisil obviously stood up and played extremely well in his first two matches here," Hewitt said.
"So you're probably assuming that they're going to put him in. He's done everything right so far.
"And then Denis has played quality matches in both his singles as well.
"Both of those played really good doubles. So whether Felix fits in to that or not, that team tomorrow night, I'm not sure.
"All I can control is obviously our boys and getting them prepared as well as possible and working out game plans for them to hopefully go out and execute and give ourselves the best chance.
"But we're certainly not taking anything for granted. It's going to be a really tough three matches."
Canada's decision to forfeit their match could have repercussions for the make-up of the Davis Cup quarter-finals.
With the two best runners-up from the six groups earning a spot in the quarter-finals based on the number of ties, sets and games won.
Novak Djokovic was critical of the Canadian move and also the ITF's decision to award such a comprehensive scoreline given the rules of the competition.
"I personally don't like that," Djokovic said.
"That shouldn't be allowed. I understand that Canada is through already.
"Maybe they wanted to rest their injured players for the quarter-finals and onwards?"