Nadal was warned by the umpire for what the official felt was receiving advice from his uncle Toni, who was in the stands during Nadal's difficult five-set victory over Philipp Petzschner of Germany.
But Nadal angrily denied the allegation and promised to take it up with Wimbledon officials, The Sunday Telegraph reported.
"Toni wasn't giving me any tips, he was only supporting me," Nadal said. "Sometimes in the past Toni would talk, maybe too much, and the referee or the umpire would give me advice and, if it continued, a warning, but he didn't talk too much this time in my opinion."
The illegal coaching allegations have been the buzz of Wimbledon during the weekend, the Telegraph said.
The tournament resumes Monday. Defending seven-time champ Roger Federer will play Austria's Jurgen Melzer for the first time, while Novak Djokovic faces a challenge from Australia's Lleyton Hewitt.
On the women's side, a rematch of the 2004 final between Maria Sharapova and Serena Williams promises to be the highlight.