Grosjean was forced to look on over the course of the Italian Grand Prix weekend as he served a one-race ban for causing a pile-up at the first corner of the event in Belgium a week previously, taking out four cars.
Given the Frenchman had been involved in a number of early-race incidents this season the stewards at Spa-Francorchamps made an example of Grosjean, who became the first driver in 18 years to be handed a ban.
Watching reserve Jerome D'Ambrosio replace him at Monza will likely have grated on Grosjean who will return to the cockpit for the next race in Singapore in 12 days' time.
"He will have learned a lot because being in your car you have only one radio in your head," said Boullier.
"When you are sitting in the garage and you have both cars then you can learn much more.
"He has definitely learned his lessons and I know he is extremely eager to get back in the car in Singapore."
In contrast, team-mate Kimi Raikkonen continues to make steady progress, almost unnoticed.
A difficult weekend for Lotus on a track not suited to their car saw Raikkonen claim fifth to move up to third in the standings, one point behind second-placed Lewis Hamilton and 38 adrift of championship leader Fernando Alonso.
Boullier added: "We knew from past history, and from this year, we would not be on top form at Monza, that it would not be easy."
Asked whether Raikkonen, still to win a race this year, was taking the title by stealth, Boullier replied: "It's good for us, good for Kimi.
"The approach he has is good. The more we can deliver big points, and if we can maintain our consistency, that is going to be key for the championship.
"We have said this since the beginning (of the season) and he is confirming that now.
"So we look forward to the next races because they should suit our car much better."