Cameron Norrie needs a shock win over Novak Djokovic to keep alive Great Britain's hopes of beating Serbia and reaching the Davis Cup semi-finals.
Britain trail 1-0 in the best-of-three tie after Jack Draper lost 7-6 (7-2) 7-6 (8-6) to Miomir Kecmanovic.
Norrie faces 24-time major champion Djokovic in the second singles match.
If Norrie does earn a first career win over the world number one, the doubles match will decide which nation plays in the last four on Saturday.
"It's difficult knowing that Cam has to go and play Djokovic after, and that's seemingly a must-win match for me," Draper said.