Alexander Zverev has beaten Rafael Nadal in their opening round-robin match of the ATP Finals.
The loss dents Nadal's chances of ending the year as the number one ranked tennis player in the world.
He entered the season-finale in London with an abdominal injury.
Tuesday's match sees Roger Federer, who also lost his opening encounter, take on Italy's Matteo Berrettini.
Play gets underway at 6:00 pm UAE time.