Transport workers' leader Tony Woodley said the Birmingham car maker's planned deal with Shanghai Automotive Industry Corporation was "about jobs preservation, not job losses".
Woodley, general secretary of the Transport and General Workers Union, said business logic dictated that the Chinese would want to retain production of new models from Longbridge.
He said: "It is all to play for at the moment. The amount of jobs that stay will be determined by how much of the work we keep and how much we end up getting. I have no fears or doubts that Longbridge will be a major player. It is important that Longbridge does not just become an assembly plant."