"You challenged me in ways no one else could," Roger Federer tells Rafael Nadal, who will retire after this week's Davis Cup tennis tournament.

Williams, 40, and Federer, 41, have both announced in short succession their plans to retire, leaving the tennis world without two of its most iconic players.

At age 41, his body is telling him the time has come, the Swiss tennis great said in a video message released on Thursday. Federer has won more than 100 titles, including 20 Grand Slam singles wins.