Nadal, 32, clinched his 11th title in 14 years at Roland Garros at the weekend, beating Dominic Thiem in straight sets in the final.
The current world number one has won twice at Wimbledon but the last of his two victories came back in 2010 when he beat runner-up Tomas Berdych.
Federer will bid to defend his title in SW19 next month and secure an eighth Wimbledon title, but the 36-year-old is wary of the threat of Nadal.
Hell be in great shape for Wimbledon, Federer said of the Spanish legend.
Otherwise I havent thought too much about who could be favourite. Rafas won Wimbledon twice, so hes no one-trick pony.
Hes become better from year to year. Hes playing more aggressive and better on fast surfaces.
Hes not only the king of clay, he can play well everywhere. Then you also have [Marin] Cilic, [Juan Martin] Del Potro and, I hope, Novak [Djokovic] will come back strong.
He has already shown good tennis this year. I also hope that [Andy] Murray and Stan [Wawrinka] will come back.
Nadal was expected to step up his preparations for Wimbledon by competing at Queens next week, but he pulled out of the tournament three days after winning at Roland Garros.
Queens is a great event, I have happy memories of winning the title in 2008 and I wanted to come back this year, he said.
But it has been a very long clay court season for me with great results.
I would like to say sorry to the tournament organisers and most of all to the fans that were hoping to see me play, but I have spoken to my doctors and I need to listen to what my body is telling me.