But Lopez told France's RMC that Grosjean is safe.
"It is us who brought Romain from GP2, and his career was launched by Jean-Paul Driot, who is a friend and a partner," said the Luxembourger.
"Then the choice of the lineup for F1 was done with Eric Boullier, but it's still us who decided," added Lopez.
"And Gravity is 100 per cent ours," he insisted, referring to the management stable involving Grosjean, in which Boullier was heavily involved as the chief.
Lopez insisted: "For me, Romain is one of the best drivers in F1 today, and I think we will soon be able to announce something for the very long term."