Cristiano Ronaldo must have had good reason for walking away from Manchester United's 2-0 triumph over Tottenham on Wednesday, claims former team-mate Nani.

An excellent performance from United saw them dominate Spurs at Old Trafford, as a deflected Fred strike and a sublime finish from Bruno Fernandes gave them an important victory over a top-four rival.

However, unused substitute Ronaldo headed along the touchline and down the tunnel before the final whistle blew. According to a report in the Athletic, the 37-year-old went on to leave the stadium early too, instead of celebrating with team-mates.

Despite his side's superb display, United manager Erik ten Hag was forced to field questions over Ronaldo's premature exit after the game, telling Amazon Prime he would "deal with" the matter on Thursday.

Nani, who played with Ronaldo for United as well as Portugal, defended his former team-mate before suggesting Ronaldo likely had valid reasons for his early departure.

"I don't know what happened in that moment," Nani exclusively told Stats Perform. "Maybe he had to go to the bathroom.

"Everyone knows he is a professional, very big professional."

Nani, now playing in Australia's A-League for Melbourne Victory, did not watch United's game against Tottenham, but he knows how being an unused substitute would feel for Ronaldo, and he suggested the early walk-off was not as significant as some have made out.

"He works really hard to be on the field. Maybe [there can] probably be a little bit of frustration there on not being an option to play," Nani said.

"But this is his desire, to be on the field and play. But I think it's not a big deal because there is a reason probably."