Rudi Garcia says it is vital Lyon replace Moussa Dembele if the striker joins Atletico Madrid.
LaLiga leaders Atleti are reportedly closing in on signing Dembele on loan for the rest of the season following Diego Costa's departure.
The former Celtic frontman scored 24 goals last season but has found the back of the net just once in the current Ligue 1 campaign and is currently sidelined after suffering a broken arm last month.
Lyon head coach Garcia does not want the 24-year-old to leave the Ligue 1 club, but expects to be given the green light to go into the transfer market if he does move to the Spanish capital.
Garcia said: "He is an important player. We prefer to keep him, but we would need to replace players who leave, Moussa included if that is the case. It is logical."
Although Dembele was expected to be out until February, Garcia says he may be cleared to return earlier.
"Usually the type of injury he had means he could not play for six weeks. I think it was on the 22nd of December before we played Nantes [when he suffered the injury], so there is still time," he said.
"It is always all about what the doctor says and also the surgeon who performed surgery on him. Let's see if it could be less. We will see how Moussa reacts."