Sainz's car suffered severe damage after running over a water valve cover early in the opening session of practice.
The team had to rebuild the car around the spare chassis, and also swap the power unit and gearbox.
Unfortunately for the Spaniard, one of the damaged items was the energy store, and by taking a third example for the season he automatically triggered a grid penalty.
Vasseur tried to argue with the stewards that it was a case of force majeure but to no avail.
"Sure, I went there, and I discussed with them," he said when asked if he'd tried to get dispensation. "It's a strange feeling for us, because first, I don't think that we did something wrong.
"We have to pay a mega price for this. And on the top, you have the penalty when you know that we are fighting for the championship, and 10 places is a huge hit.
"OK, we that we have to try to avoid thinking about it, to do the job that we can come back. We have a good pace, we have to be focused on the quali, and then to do a good race. We don't have time to discuss this."
Asked if the other teams could have supported his case, he said: "I don't think that it could be a decision from the teams, to say that we allow them to do this or that. Now tomorrow if someone pushed in the other direction, it's another story."
Like Alpine with Esteban Ocon's damaged car, the team had no problem in getting around the rule that restricts a driver to using one chassis in a day.
"This was a good joke as well," said Vasseur. "You are not allowed to change your chassis during the day. But they told us you past midnight, it means that it's not the same day anymore!"
Vasseur stressed that the between-session rebuild was made possible by the two-and-a-half-hour delay to the start of FP2.
"We are not trying to have a record on this," he said. "But for sure it was a big one, because we had to change the chassis, engine, battery, gearbox, to build up a new one. It was a good job from the mechanics."
On a more positive note, Charles Leclerc topped the FP2 session for Ferrari, with Sainz in second.
"We know that it's a bit like Monaco or Baku, it's a long weekend, and we have to build up the performance over the weekend," said Vasseur. "It's not just matter to be quick in P1, but it's better to be quick in P1.
"We know that it will be about graining, but so far, so good. The track will improve much more than a normal track, it means that you have to anticipate what will be the status track for Saturday."
