Standard Sport understands that Martinez is desperate to link up with compatriot Lionel Messi at Camp Nou, with the Spanish giants looking for a long-term replacement for Luis Suarez.
Martinez's release clause of €111 million could prove problematic as the coronavirus pandemic has a crippling impact on football finances, but Moratti says the play staying put may not be worthwhile.
"You can't hold someone who has the idea of being somewhere else," Moratti told Sportmediaset.
"That would put him in a position to remain involuntarily or, in any case with a different impulse, in the same place."
Inter sporting director Piero Ausilio has warned Barcelona that only a triggering of Martinez release clause will faciliate a transfer as the club ponder part-exchanges.
"As far as Martinez is concerned, there is only one way that he will leave Inter and that is by paying his clause," Ausilio told Sky Italia.
"A clause that everyone knows – there is no point in hiding – is demanding, because it has both deadlines and commitments that must be kept very precise.
"It is a clause that expires in the early part of July so it won't last for a long time. And it is the only possibility that exists to take Lautaro away from Inter today."