In July, Ferrari president Sergio Marchionne confirmed rumours that respected designer Sassi had been either ousted from the F1 team, demoted or promoted.
"Sassi is continuing the development of his career. We did it with Cardile as well," he said.
Marchionne was referring to Enrico Cardile, who moved from Ferrari's GT programme to head the F1 aero division.
Sassi's move was in the opposite direction, but Speed Week now reports that the Italian did not want to work outside of F1 for Fiat Chrysler.
Spanish newspapers AS and Marca claim that Sassi is instead heading to Brixworth, where Mercedes designs and builds its championship winning F1 engines.
Sassi, who was replaced at Maranello from within Ferrari's GT division, worked for Ferrari for 11 years.
Ferrari and Mercedes did not comment.