The season-ending tournament has been held indoors since 2005, with London hosting the event for the past five years.
However, Nadal believes that the Tour Finals would benefit from a change of surface once the 02 Arena's contract ends in 2015.
"The Tour Finals have been indoors from 2005 until now, so I am a bit unlucky with this," Sky Sports News quotes him as saying. "For me it is more fair to have it outdoors on different surfaces.
"In this tournament we qualify by playing on all surfaces, but the Tour Finals are always on hard courts.
"I say it for the next generation and because it would be interesting for the fans."
Nadal gets his campaign underway on Tuesday when he takes on fellow Spaniard David Ferrer.