Rafael Nadal forced to sit out of ATP Cup tie against Alex de Minaur due to back injury

Rafael Nadal has been forced to withdraw from his clash with Australian Alex de Minaur tonight after the world No.2 was unable to overcome a lower back injury.

Nadal was scheduled to take on de Minaur as part of Spain's opening ATP Cup tie.

Roberto Bautista-Agut will now face de Minaur in the second singles tie, with Pablo Carreno-Busta facing to meet John Millman in the first singles tie.

According to Nadal, he is suffering from a "stiff low back" and as a result will not take to the court, with the hope he will be right to play on Thursday.

"Hi all, we have decided with Team Spain and my team, to not play today the first match of the ATP Cup here in Melbourne since I have a stiff low back," he tweeted.

"Hopefully I'll be better for Thursday. We have a strong team, all the best to (Pablo Carreno-Busta), (Roberto Bautista-Agut) and (Marcel Granollers)."