Federer, who defends his title in London, could be excused for thinking life would be easier without the injured Rafael Nadal.
But with Spanish No 2 Ferrer edging ahead of the Swiss with a seventh title of the year in Paris, the 30-year-old knows he will have to bring his A-game to the capital.
"Obviously the big (question) was whether Murray going to be in my group or not I guess," he said.
"Now that Nadal is not here you feel that maybe Ferrer is not Nadal, so it's better to have Ferrer in the draw.
"But then again Ferrer has had his major upsets at the World Tour Finals. I played him once in the finals and once in the semis and they were indoors.
"Normally we think Ferrer is not the best indoor player - but he has just won Valencia and he might win Paris (which he did) so it's overall a tough group for both of us and all players and it's exciting.
"That is why we come here and play and that is why the fans come out to watch."