American John Isner only found out last week that he would be playing at the ATP Finals in London after world number two Rafael Nadal withdrew through injury.
The 33-year-old will be aiming to add to the two titles he has won this year.
His opponents in the Guga Kuerten group for the round-robin stage are Novak Djokovic, Marin Cilic and Alexander Zverev.
He starts his campaign against Djokovic on Monday (not before 20:00 GMT).
READ MORE: Federer goes for 100 at ATP Finals