Del Potro was drawn in Group B with defending champion Roger Federer, who will lose the number one ranking to Djokovic on Monday, fourth seed David Ferrer and eighth seed Janko Tipsarevic.
Murray's group looks significantly tougher but he played down the differences, saying: "Indoors Roger has been the best player over the last couple of years.
"Juan won two tournaments indoors just before Paris. If everyone plays their best tennis, I don't think one group will necessarily be tougher than the other."
Murray has been reunited with coach Ivan Lendl this week for the first time since that momentous night in New York.
Lendl only travels with his charge for certain tournaments and stayed at home in the US while the Scot played in Tokyo, Shanghai and Paris.
Murray, who is making his fifth appearance at the Tour Finals, said: "I always enjoy having him around. He's been a great asset to me and all the guys I work with.
"He's been very easy to work with and helped me and everyone at the big events this year and he's helped me come back from some tough losses and finish the year in the slams very well. I hope we can have a good tournament."
