One of the NBA's all-time icons – San Antonio Spurs center Tim Duncan – is leaning strongly toward retirement, a decision that would end an illustrious 19-season NBA career, league sources told The Vertical.

Tim Duncan has won five championships with the Spurs. (Getty Images) More

Duncan has left team officials, close associates and friends with a strong belief he's preparing to make an announcement in the near future on his departure, sources said.

The Spurs reached agreement on a two-year, $30 million-plus deal to sign Pau Gasol, league sources said.

Duncan recently elected to exercise the $5.6 million player option on his 2016-17 contract – a payment the Spurs could still make to Duncan regardless of whether he plays or retires.

Duncan – a five-time NBA champion, three-time NBA Finals MVP and two-time regular-season MVP – would be remembered as one of the great winners and leaders in NBA history.

For his career, Duncan has averaged 19 points and 10.8 rebounds. In 61 games last season, he averaged 8.6 points and 7.3 rebounds in a little more than 25 minutes a night.

The Spurs lost to the Oklahoma City Thunder in six games in the Western Conference semifinals.

Duncan, who has long had trouble with his left knee, was slowed during the season with soreness in his right knee.