It is the first year since 2002 that the 32-year-old has not made a Grand Slam final and sparked feverish speculation over his future in the sport with the loss to Robredo coming on the heels of a second-round exit at Wimbledon.
Give him a break"Roger did not play close to his maximum level so it's always a question of why is he not playing well. People need to give him a break a little bit, because I think it's normal to expect that he's not moving as well as he did when he was No. 1 and he was so dominant," said the Serb.
"For me, he's still playing really well and definitely deserves to be one of the top five players in the world, no question about it."
Djokovic said he would not be advising Federer on what his future plans should be despite his rival having slipped to seven in the world, his lowest ranking for over a decade.
"How long he's going to play? That's a question for him. But he's what, 31, 32 years old? Tommy Haas is 35 and close to the top 10. So I think people are seeing Roger always being a top three, top two guy and competing for Grand Slam titles. That's not happening, and all of a sudden it's a huge surprise."
World number three Andy Murray said he was surprised to see Robredo beat Federer for the first time in 11 meetings.