"It was an internal fight. My head said I think you should retire, I kept saying that over and over but my heart was keeping telling me that I would be better to continue playing and compete," said Ballesteros at the site of this year's British Open in Scotland.
"I probably made the most difficult decision of my career as a player and I decided to retire."
Ballesteros, 50, has played in two tournaments this year, missing the cut at the Masters and finished tied for 77th in a Championship Tour event. He denied rumors of ill health and a suicide attempt.
Ballesteros, who turned pro in 1974, played in his first British Open in 1975 when it was at Carnoustie, as it is this week. He won the tournament in 1979, 1984 and 1988. His Masters' titles came in 1980 and 1983. His five major victories were included in his nine total PGA tournament titles. He also won 49 European PGA Tour events.