Krish Bhaskar, who runs the Motor Industry Research Unit, said he feared for the future of Lotus's world-renowned engineering business after the company announced 350 job losses.
Lotus announced the redundancies after losing an engineering contract and the ending of several other projects.
He said Proton should act now to support the company.
"I am surprised the Lotus engineering business has done so badly as there is a need for outsourcing in the motor industry," he says. "What concerns me is that the job losses may mean that the engineering business falls below the critical level needed to win contracts. They just won't have the capability any more.
"I believe that it is just not visible enough around the world, it needs Proton spending the money to promote its capability. Lotus as a brand is worth millions and Proton is letting it die."
In a statement, Lotus said: "The motor industry is changing dramatically around the world in all areas, particularly in the engineering sector. Group Lotus has always managed its business carefully to meet those changes in line with demands for its products and services.
"Recognising the business has to change, the board of directors regrets it is necessary to downsize the UK operation through all areas of the business other than direct manufacturing staff. This is a direct result of the completion of existing activities and the loss of a major consulting project," said the statement.