World number one Rafael Nadal admits his 17-tournament schedule in 2017 was too demanding and he is likely to reduce his commitments next year.
The Spaniard, who is scheduled to make his return to action in the Brisbane International, a tournament that is live on BT Sport 1 & BT Sport 3 from Sunday 31 December, has not played competitively since withdrawing from the ATP Finals in London last month after losing to David Goffin in his opening match.
He had also pulled out of the Paris Masters earlier in the month with the same injury.
Nadal travelled to Barcelona earlier this week for an assessment of the injury and cancelled a five-day training camp in Mallorca.
The 31-year-old also pulled out of a lucrative exhibition tournament in Abu Dhabi which he was to take part in on his way to to the Brisbane International and has yet to make a decision on Brisbane and the build-up to the Australian Open, which begins on 15 January.
The 15-time Grand Slam winner, speaking to Spanish broadcaster TV IB3 after being named best athlete of the Balearic Islands for 2017 said: 'It was a tough 2017 and I need to take my calendar in a different way in order to be ready.
'At the end of the season knee bothered me and we are working so that it hurts me less. We have to see how things progress everyday in order to know when I will make my first appearance in 2018.' But what will be his first tournament of the season? 'It will be official when it will be official.
"I always respect my commitments and try to adhere to them, but sometimes things do not work the way you wish for and the recovery is slower."
Nadal overcame an injury-stricken 2016 to reach the final in Australia last year before going on to win the ATP title on clay then his tenth French Open and later his third US Open.
He finished the year as the oldest man to hold the No.1 spot in the ATP rankings.
The Brisbane International at the Queensland Tennis Centre is live on BT Sport 1 & BT Sport 3 from Sunday 31 December 2017 until Sunday 7 January 2018.
Image: Getty Images/ Julian Finney
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