The Swiss says, "you can't just repeat a year like this," in reference to Djokovic's 2015 season.
Federer and the Swiss team were aided by the Bryan's coach before their Davis Cup final last year.
The final is set to begin on Friday in Ghent, 35 miles from Brussels.
The world No. 48 has not completed a match since the U.S. Open.
The government has warned of potential attacks in Brussels, 35 miles from the fiinal's location in Ghent.
How two points from the O2 final defined Djokovic's and Federer's seasons.
Previewing and predicting Saturday's semis at the World Tour Finals in London.
Jelena Jankovic and Ana Ivanovic continue to fascinate us after all these years.
Examining Rafael Nadal as his disappointing season winds down.