Both players sat out Monday's win at Lecce as Koopmeiners attempts to force through a move to Juventus, with Lookman doing the same regarding PSG.
Percassi said: “I always reaffirm what my father says, we are Atalanta, we must retain our identity and have clear objectives. It is also true that last season, for the first time, the coach, club and directors aimed to keep all the big plyers who were the protagonists of an extraordinary campaign with Atalanta.
“That was the idea, to confirm all our first-choice players. We were aware there could be turbulence on the transfer market. We didn’t expect certain things to happen, but the club is prepared to invest, if there are opportunities then we are prepared to take them, and we’ll see what happens over the next few days.
“We are very relaxed because our idea, shared by coach, club and owners, was for the first time in our history not to let these important players go. We as a club have always respected our commitments and we cannot wait for this transfer window to close, as it reserved a few ugly surprises too, like Gianluca Scamacca’s injury.
“All players belong to Atalanta and the club will decide what to do for the good of this team.”
He also said: “Unfortunately, too often these lads are given bad advice. The fact the transfer market is open when games are played frankly makes it feel like it’s infinite. We had tried to regulate the timing of these things over the summer, but it was not possible because the Saudi Arabian leagues wanted an extension.
“I do feel this needs to be regulated better.”