Rafael Nadal pulled out of Spain’s opening ATP Cup tie with a lower back problem less than a week before he bids for a record 21st men’s Grand Slam title at the Australian Open.

The world number two, 34, was scheduled to face Australia’s Alex de Minaur at Melbourne Park on Tuesday.

Nadal said he hoped to play for 2020 runners-up Spain against Greece on Thursday.

Novak Djokovic earlier gave defending champions Serbia a winning start.

World number one Djokovic beat Denis Shapovalov 7-5 7-5 as Serbia claimed a 2-1 win over Canada in their opening Group A match.

Milos Raonic had put Canada ahead with a 6-3 6-4 win over Dusan Lajovic but Djokovic and Filip Krajinovic won the doubles match against Raonic and Shapovalov 7-5 7-6 (7-4).