Rafael Nadal has called for a merger of the ATP and Davis Cup after his loss to Novak Djokovic, stating that having two "world cups" within such a short time was a "confusion for the spectators".

Nadal pulled out of the doubles in the eleventh hour, leaving Pablo Carreno Busta and Feliciano Lopez the task of beating Serbia, who were ultimately crowned ATP Cup champions.

Nadal said he was unable to play in the doubles decider for his nation due to physical exhaustion. Credit:Getty Images

The world No.1 said he made the decision to negate the decider due to a lack of energy, citing the consecutive world cups as the reason for his exhaustion.

"I can't change my mind that two world cups in one month is not real," he said after losing to the world number two. "For the health of our sport and for the benefit of our sport it is, in my opinion, mandatory that we fix it."