Kimi Raikkonen's Australian Grand Prix victory announced Lotus as a championship contender this year.
The team then slipped back in Malaysia, finishing only sixth and seventh, with Grosjean ahead.
Lotus remains second in the constructors' championship, 26 points behind Red Bull, while Raikkonen is Sebastian Vettel's nearest rival in the drivers' table, nine points adrift.
Asked if he was confident Lotus could stay in the title hunt, Grosjean said he was confident in the team's capabilities but unsure about its resources.
"It depends on the money that we have. That is the key in F1," he said.
"We know we have good people, we know they are able to do a race winning car, we know that on development and on factory tools we are there.

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