Sanchez is leaving his job as Head of Vehicle Concept and Head of Operations of the aerodynamic sector, Sky Sports Italia report.
He was the top brain behind last season’s F1-75 - which was blighted by reliability problems - and this year’s SF-23 which is off to a worrying start.
Leclerc was told of Sanchez’s decision during preseason testing in Bahrain and was left “visibly dissatisfied”, Sky Sports claim.
He must go through a period of gardening leave before rejoining McLaren, the team he left to join Ferrari in 2012.
Ferrari got rid of team boss Mattia Binotto over the winter, replacing him with Vasseur, but this latest change is an early setback for them.