Federico Gastaldi says Lotus need to "start looking now" for a replacement for Romain Grosjean have been caught out by his decision to leave.
This coming Tuesday new team Haas F1 are expected to announce that the Frenchman will lead their charge in their debut campaign.
Grosjean is believed to have opted for Haas in order to take a step closer to a possible Ferrari drive in 2017.
His decision, though, has come as a surprise to Lotus with F1i.com reporting that deputy team principal Gastaldi only learnt of his pending move on Sunday.
Asked if Lotus were already talking with other drivers, Gastaldi said: "No, we have to start looking now.
"We obviously had Romain and Pastor [Maldonado]. Romain has been with us for seven years on the Gravity program.
"For me personally and I’m sure for the whole team it will be sad to see him going because he’s been part of the family.
"He has developed himself in the right direction. He’s smart, he’s quick, he’s committed and he has a strong head.
"Now we have to start working to get another driver."
Grosjean's departure does not mean an automatic promotion for reserve driver Jolyon Palmer although Gastaldi says he is definitely in the frame.
"[Palmer] could perfectly be an option. He is our driver and we just need to see what he wants to do.
"But I only found out last Sunday when Gerard Lopez was in Singapore and now we have to see the timing, we have to see the final documentation, what Romain wants to do. He obviously is still with us until the end of the season.
"If you ask me about Jolyon, he could be perfectly the second driver. He’s a very good driver, he doesn't need any presentation. He’s the GP2 world champion, for me he’s a fantastic driver, he’s smart, he’s a fantastic marketing tool, he’s young. Why not?"