"He can't seem to control his exuberance. If he hits four fours in an over, he wants to hit a fifth one," Vengsarkar said on Monday.
"As one of the seniors in the team, he should be able to play longer innings." Sehwag failed to build on starts of 30 and 21 in the first two one-day internationals in Bangladesh last week which India won to take an unassailable lead in the three-match series.
The final one-dayer is on Tuesday.
"I'm disappointed with his performance," Vengsarkar told Hindustan Times newspaper.
"He has so much talent. But he's wasting it."
A fierce striker of the ball, the 28-year-old Delhi batsman made a name as a destructive batsman, but a prolonged slump in form has led to him being dropped from the Test team for the two-match series in Bangladesh starting from May 18.
