Britain's Andy Murray says it will "be tough" to play in Saturday's Davis Cup doubles after losing a marathon five-hour singles match against Argentina.
The world number two was beaten in five sets by Juan Martin Del Potro, while Kyle Edmund also lost as Argentina went 2-0 up after day one in Glasgow.
Murray and his brother Jamie are set to play doubles at 14:00 BST, but line-ups can change an hour before the start.
"I'll have to see how I feel when I wake up in the morning," said Murray.
"I've never played a match that long.