The crash came after a poor start to the season, only managing to score a single point before the summer break at the Austrian Grand Prix.
He looked to be set for a career-best ninth place finish in Spa, that was until he made an error on the penultimate lap and lost the car into the barriers.
"It was a big shock for everybody in the team because it was a good opportunity," Vasseur told Autosport.
"Antonio came back from nowhere, and on one of the last laps he had the crash.
"We had a tough discussion with Antonio, because these kind of things can decide your career. We were thinking about the future.
"We had to sit down the week after and we had to discuss about the situation, and he had a very good reaction."
Vasseur went on to say that the Italian driver had a turning point in Monza, where he finished P9 to score two points in front of his home crowd.
"I think he did a very good job, the pressure was there. In my mind it was very important how Antonio reacted in Monza, that was the real push.
"The issue for Antonio was we were down on performance when he was on top. You can be in front of your teammates but [it's noticed less] if it's for P14 or P15. If it's sixth or seventh, everyone's speaking about you.
"One thing is to show to the team and the other one is to score points because for you, for the paddock, everybody is just focused on results."
Bahrain International Circuit - Winter testing