Parun also believes Federer can not be considered the greatest player of all time if he does not have a French trophy on his mantelpiece.
Nadal is closing in on Bjorn Borg's record of six French Open titles after a 6-1, 6-3, 6-0 win against Federer yesterday.
The Spaniard again proved his mastery on clay as he pummelled the Swiss star in straight sets in one of the most one-sided finals in the Open era.
Parun said Nadal's speed was his greatest asset on clay.
"First of all, clay is much slower but the ball bounces up quite high. Both those factors suit Nadal down to the ground," Parun told the Otago Daily Times yesterday.
"He's probably the fastest person in tennis. There's no ball that he can't run down. He's got an incredible will to win and refuses to give up on any ball.
"You think you've hit a winner but the ball comes back. And that's very frustrating to a lot of players. He reminds me a lot of Roy Emerson.
"Nadal is undoubtedly one of the great claycourt players of all time. I always regarded Borg as the best I've seen and Nadal comes very, very close to him."
Parun won the French Open doubles title with Australian Dick Crealy in 1974 and was a singles quarterfinalist a year later.
He described Nadal as a relentless baseline attacker - the prototype of a good claycourt player.
Nadal's top-spin forehand bit the clay and bounced too high for Federer to easily counter.
And Federer made the mistake of thinking he could beat Nadal from the baseline.
Parun does not think Nadal can beat Federer at Wimbledon because he has a relatively weak volley.
Talk of Federer being the greatest player of all time was premature, Parun said.
He ranked both Bill Tilden and Rod Laver ahead of the Swiss.
Federer will remain at No 1 in the world rankings.
He was 1000 points clear of Nadal before the French Open and, while Nadal gets 1000 ranking points for winning a grand slam, Federer gets 700 for reaching the final.
The King of Clay: Rafael Nadal
• Won his fourth consecutive French Open.
• Did not drop a set at the tournament.
• Is a perfect 28-0 in matches at Roland Garros.
• Has won 122 of his 126 games (96.8%) on clay since 2005.
• Has beaten Roger Federer eight times out of nine on clay.
Clay v grass
• Rallies last longer on clay, so fitness is a key.
• Balls are slower on clay but bounce higher.
• Balls are quicker on grass but bounce lower.
• Clay suits athletes and good top-spinners (Nadal, Bjorn Borg, Roy Emerson).
• Grass suits tacticians, hard hitters and good servers and volleyers (Federer, Pete Sampras, John McEnroe).
