Spanish tennis star Nadal, 32, was pictured wearing boots and white gloves, mopping up the floor of a warehouse on Wednesday on the island where he lives.
The 17-time Grand Slam champion, currently sidelined through injury, has also offered to open up his sports centre and tennis academy to people made homeless by the floods.
“I know how important Mallorca is to Rafa and I have been in touch with him to see if I can help with anything,” Federer said in a video message recorded in Shanghai where he is currently competing.
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“I have seen him helping in the village where he comes from and to see that is super-inspiring. Rafa, you have our support.
“We are thinking of all the people in Mallorca. We wish you strength in these difficult times and I hope to be back on Mallorca soon.”
Fellow rival Novak Djokovic, also taking part in Shanghai, said he hoped Nadal's efforts would inspire others.
“A big hug and friendly regards to Rafa and well done amigo for helping out,” said the reigning Wimbledon and US Open champion.
“I invite anyone to give their support in anyway they can. Gracias.”