He then had an early exit in Australia, sliding out on the opening lap following contact with Lance Stroll.
It leaves the Monegasque driver level with Nico Hulkenberg in the drivers' standings with six points.
At the same point a year ago, he led the world championship with two wins from three starts.
“I have absolutely no doubt about the motivation of Charles,” said Vasseur.
“You know that for sure the start of the season is not the goal that we had; the DNF in Bahrain and then the penalty in Jeddah, and the DNF in Melbourne.
“For sure it was not at all the plan, but the motivation is there.
“I have a good relationship with Charles and this won't affect the mood.”
Vasseur can understand his driver's disappointment and suggests it's an appropriate reaction when speaking to the media post-race.
“For sure when you are jumping on Charles, Pierre [Gasly], [Fernando] Alonso, or other drivers in the TV pen 30 seconds after the race, for sure they can't be happy and I would be very frustrated if they were relaxed and happy with the situation.
“The most important [thing] for me is to keep everybody motivated, pushing in the same direction, and they are supporting the team.
“The motivation is not an issue at all.
The Italian squad heads to the Azerbaijan Grand Prix fourth in the constructors' championship on 26 points.
Red Bull heads that competition, already 97 points clear of the Scuderia.