For 1999, Diniz partnered experienced driver Jean Alesi at Sauber. He endured a torrid start: He was forced into retirement in the first five races held in the season; and in the sixth race of the season held in Canada, he managed to score his first point of the season with a sixth-place finish. Diniz suffered a retirement at the next round in France, before clinching consecutive sixth-place finishes in the next two races and later suffered further consecutive retirements in the following six races. In late August, it was announced that Diniz would remain at Sauber for 2000. At the European Grand Prix, Diniz was hit by Benetton driver Alexander Wurz who sent the Sauber driver into a barrel roll and suffered a bruised knee and shoulder, resulting from his car's roll hoop becoming damaged. The season was somewhat of a disappointment for both the team and the driver, however although Diniz only finished four races all season he scored points in three of them. Diniz finished the season fourteenth in the Drivers' Championship and scored three points.