Concise News understands that Djokovic last played in the last four at Roland Garros in 2016.
Djokovic, 32, won 7-5 6-2 6-2 in their rain-delayed quarter-final.
Zverev, 22, failed to serve out the first set and it proved pivotal as Djokovic dominated from then on.
The 15-time Grand Slam champion will play Dominic Thiem in the last four.
Thiem, last year’s beaten finalist, beat Russian 10th seed Karen Khachanov 6-2 6-4 6-2 to reach the semi-finals.