Rafael Nadal has once again been forced to withdraw from a tournament this week, missing the ATP Finals to continue a worrying trend for the Spaniard in hard-court tournaments.

An abdominal problem forced Nadal to abort his planned comeback from a knee injury at the Paris Masters as he ceded the world number one ranking to Novak Djokovic and he has not recovered in time for London.

Nadal did win the Rogers Cup in Toronto this season, but he has otherwise endured nothing but misery in this year's biggest hard-court events.

We look at the problems that have contributed to the Spaniard completing just one major hard-court competition - that successful campaign in Toronto - in 2018.

HIP ISSUE ENDS AUSTRALIAN OPEN HOPES

The beaten finalist at Melbourne Park in 2017, Nadal saw his Australian Open campaign end in painful fashion this January.

A hip injury proved increasingly problematic during his quarter-final against Marin Cilic and the top seed cut a frustrated figure as he retired trailing 2-0 in the fifth and final set.

The issue was serious enough to also rule Nadal out of the Masters 1000 events in Indian Wells and Miami, but he went on to enjoy familiar success on clay, including yet another French Open title.

ANOTHER SLAM, ANOTHER RETIREMENT

After his success at Roland Garros and a run to the semi-finals of Wimbledon, Nadal did enjoy hard-court success, beating Stefanos Tsitsipas in the final of the Rogers Cup . However, he has not completed a tournament since.

Nadal withdrew from the following week's Cincinnati Masters and was then forced to bring a premature end to his US Open semi-final with Juan Martin del Potro due to a knee injury.  

He remained absent as the Shanghai Masters took place earlier this month.

COMEBACK DELAYED UNTIL 2019

Having recovered from his knee problem, Nadal was set to return to action in Paris.

Instead, an abdominal injury resulted in him missing another Masters 1000 event, his fifth absence from such a tournament this year.

And Nadal was not able to recover to play the season-ending ATP Finals, opting to undergo surgery on a long-standing ankle problem in order to rehabilitate before 2019.

NADAL'S 2018 RECORD IN HARD-COURT GRAND SLAMS/MASTERS 1000 EVENTS/ATP FINALS

WINS - 1 (Toronto)

RETIREMENTS - 2 (Australian Open, US Open)

DID NOT COMPETE - 6 (Indian Wells, Miami, Cincinnati, Shanghai, Paris, ATP Finals)