The Frenchman struggled in the first three races of the year, but responded to secure a third-place finish in the Bahrain Grand Prix last time out.
"If you look at the season so far, except for the car issue, he didn't have troubles. He was having good starts, good first laps and good overtaking manoeuvres. So I think he is okay now," Boullier told AutoSport.
"But Bahrain was a big relief. He put a lot of effort in to rebuild himself after 2012, and it is now paying off. He had a frustrating first three races, but he can now build on this and keep the momentum."
Sebastian Vettel claimed first position in the race.