Nadal casts doubt over participation

Spain's Rafa Nadal said he cannot guarantee he will make the trip to Melbourne for next month's Australian Open after returning to action at the Mubadala World Tennis Championship in Abu Dhabi.

The 20-times Grand Slam champion's comeback at the exhibition event -- his first tournament appearance since the Citi Open in Washington in August -- ended in two close defeats by Andy Murray and Denis Shapovalov.

Nadal, 35, spent four months on the sidelines with a foot injury. He was knocked out at Roland Garros in the semi-finals and was forced to pull out of Wimbledon, the Tokyo Olympics and the U.S. Open. "The idea is to go there and try my best there in Australia... Being 100% honest, I can't guarantee it," Nadal said. World number six Nadal said he would not have returned to tennis if he did not feel he was competitive enough.

The Australian Open begins on January 17.