Roger Federer feels the "unbelievable" environment London provides for the ATP World Tour Finals makes a potential return to New York difficult.
The end-of-season showpiece has been held at London's O2 Arena since 2009, having previously been staged at New York's Madison Square Garden for 12 years between 1977 and 1989.
2015 represents the last year of the O2 Arena's contract to host the Finals, leading to speculation that the tournament could move on.
"I think if we come here, everything needs to be right - the time, the money," six-time winner Federer said after an exhibition match against Grigor Dimitrov at Madison Square Garden on Tuesday.
"In London, we have an unbelievable tournament going on right now, so it needs a lot, in my opinion, to move away from the O2, which is a wonderful venue.
"It's sold out, every single session, day session, night session, and it's very, very successful. I don't know what the ATP's going to do with it, but it's our jewel of the ATP Tour and a lot of thought will go into it.
"I would love to see the year-end championships in a strong market, in a cool city, and clearly New York fits the bill for that but still I think a lot needs to be done."