Andy Roddick's competitive spirit in the early years of his career has been revealed by Serena Williams' former coach Rick Macci.

Former World No. 1 Roddick achieved a lot in his career, winning the 2003 US Open title on home soil and reaching three Wimbledon finals. The American also has 32 ATP titles to his name and was No. 1 in the ATP Ranking for 13 weeks in total.

On a recent episode of the ATP Tennis Radio Podcast, prominent tennis coach Macci, who has worked with the likes of the Williams sisters and Maria Sharapova, revealed that Roddick's competitive nature was the strongest he had ever seen.

"I did work a lot with Christian Ruud, Vincent Spadea, there's been other guys who didn't become top 10 in the world. But Roddick, his thirst for competition was like no other. The guy was so brutally competitive," Macci said.

The 68-year-old went on to praise this competitiveness, saying that it helped Roddick with handling pressure.

"First to get the drink, there would be a smack on the table, he would fight you to get it. When he lost, he would keep bugging me... I said, you gotta earn it. He would come back the following day, I would play him... The wiring to compete, which is the wildcard to handling pressure. When you're all about the competition, you don't choke as much, get as nervous," he continued.

Macci also lauded another aspect of Roddick's game as he called the 41-year-old's forehand 'one of the best in tennis history.'

"His forehand.. he kinda taught me about the racket going on the outside, the elbow elevated, the pull, the flip, it was a little weird when I saw it work. Then he became biomechanically one of the best in tennis history," he explained.