But beyond the obvious natural curiosity, the 31-year-old with 17 Grand Slam titles has plenty on his own plate as he begins a run of events this week to be followed by the Dubai Open and the Indian Wells Masters next month in California.
"I'm happy to see him back and playing on the Tour," said the two-time Rotterdam champion.
"He seems to have good energy. I was surprised he lost a final against a player ranked outside the top 50.
"I'm sure he got a lot of information about his game last week (in Chile). He knows now how much strain he is putting on his body and how he is dealing with it."
After seven months away recovering from tendon damage in his left knee, Nadal lost both the singles and doubles finals at the VTR Open in Chile.
Singles winner Horacio Zeballos could only repeat what Nadal had been saying - that his comeback would need time.
While Nadal plays on clay in Sao Paulo, Federer will be bidding to make it a trophy hat-trick in Rotterdam, when he begins in the first round against Slovenian Grega Zemlja. (AFP)
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