Grosjean produced another sterling drive in the Japanese Grand Prix to finish third behind a Red Bull one-two as Sebastian Vettel led home Mark Webber for his fifth consecutive victory.
In the early stages of the race at Suzuka, Grosjean even suggested a win was on the cards as he led for 26 of the opening 28 laps around the first pit stop.
Vettel's pace and Red Bull's strategy, however, were too much for Grosjean, who also succumbed to Mark Webber on the penultimate lap to slip to third.
Despite that, the Frenchman is currently proving he is ready to lead the team with Kimi Raikkonen heading to Ferrari.
Grosjean has out-qualified Raikkonen at five of the last six races, and was comfortably ahead of the Finn in Japan, and now Lotus are ready to take up an option on his contract.
"He did a great job," said Boullier.
"He is at the level we expected, what we have wanted him to do.
"We wanted him to establish himself as a driver like he is now, and on top of that, since Kimi announced he was leaving, it has been up to him to step up, and he has done that."
With regard to the option, with a deadline understand to be at the end of the month, Boullier added: "I need to get written confirmation from my board.
"Romain has a contract with us for next year. He has an option to be taken up, and we have to do that in a few days, so we will see."
Much depends on the deals Lotus are putting together, notably the 35 per cent stake being taken up by a consortium of investors now known as Quantum Motorsports, formerly Infinity Racing.
Lotus are also chasing Renault as not just their powertrain supplier from next season, but also as a sponsor.
Once the finances are in place then Lotus can finally go ahead and sign their drivers, including Hulkenberg who was sixth at Suzuka to follow on from his fourth in Korea a week earlier.
"Since he has been talking to us he has been doing a good job," joked Boullier.
The Frenchman added: "With the deals, we are are edging in the right direction, but until things are signed and confirmed, we will see.
"Everything should fall in place soon, and when they do we will start to tick the boxes, and the engine is on the list of what we have to confirm."
When the deals are done then Boullier will be able to make a decision on his drivers as he said: "I would love to. He (Hulkenberg) is our choice."