Spaniard Nadal has been on a spectacular run since returning to competitive action at Vina del Mar in February after a frustrating seven months on the sidelines due to a recurring knee problem.
The 27-year-old has claimed nine singles titles, including a record eighth French Open crown and five Masters events. He is bidding for his second U.S. Open triumph after beating Djokovic in the 2010 final.
"The knee is what it is and I think Rafa has grown used to playing in pain," Toni Nadal told Spanish radio station Cadena Ser on Monday.
"I think he deserves all that he has for what it costs him to achieve what he has achieved," he added.
"We couldn't have imagined six months ago when we started again ... that we would be where we are now today.
"Things have gone much better than expected and all we can do is be happy and thank God or Mother Nature or whoever for all that has happened."
Nadal and Djokovic are set to play each other for a 37th time on Monday, a record for the Open Era.
Nadal has a 21-15 winning record against the Serb and has won seven of their 10 meetings at grand slams, although Djokovic, who beat Nadal in the 2011 U.S. Open final, leads 11-6 on hard courts and 3-2 in slam finals.
"I think it's going to be a tough match and I hope that is the case for both players," Toni Nadal said.
"He is the opponent you least want to play, the world number one, and he is playing on a surface that theoretically is more favourable to him."
After the final, Nadal will fly to Madrid to represent Spain on his favoured clay in this weekend's Davis Cup World Cup playoff tie against Ukraine.
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- Toni Nadal