Kylian Mbappe has a release clause in his Monaco contract that will cost "a lot of money" to trigger, sporting director Antonio Cordon has told Cadena Cope.
Forward Mbappe, 18, has produced a string of outstanding performances to help Monaco top Ligue 1 and reach the Champions League semifinals.
Real Madrid, Manchester City and Manchester United are among the clubs tracking Mbappe, with reports in the Spanish media suggesting Madrid could offer in the region of €100 million for him.
Mbappe signed his first professional contract just over a year ago, and Cordon said that deal included a release clause.
"Yes, he has one -- but it's a lot, a lot of money," he said. "I didn't do Mbappe's contract and I can't tell you the details of the clause, but it's a lot of money.
"I hope he'll stay because we have to keep our best players, but we all know the market and how things happen. I don't know how many offers there are for him."
Prince Albert of Monaco, who remains involved behind the scenes at the club, told RMC he hoped Mbappe would stay for another season.
"I know it'll be difficult, but I think he's already talked about this," he said. "I think it's wiser, at least for another season, to stay with Monaco and for him to be a little more protected than at a big club.
"We're going to do everything to keep him a little bit more."
Former Monaco and Barcelona midfielder Ludovic Giuly said that the teenager will remain at his current club for the next year, but admitted he has the ability to play for Europe's biggest clubs.
"He has no limit at all," Giuly said at Friday's Champions League semifinal draw. "You cannot say how far he can go. Next season he will play at Monaco. For sure."
Meanwhile, Monaco goalkeeper Danijel Subasic told 24 Sata that Mbappe had suffered a tough time in the 4-1 Coupe de la Ligue final defeat to Paris Saint-Germain.
"Thiago Silva didn't leave Mbappe alone from the first to the last minute," Subasic said.
"It was tough. He was angry and wanted to destroy his confidence. In the dressing room, we saw Mbappe was very sad, on the verge of tears.
"He was very low, we felt sorry for him. I comforted him, I told him that everyone had seen how good he is and that it will continue for him. We all didn't play well that evening."
Blancos coach Zinedine Zidane recently confirmed that his club had tried to sign Mbappe as a 15-year-old before he moved to Monaco, and skipper Sergio Ramos said before the recent France-Spain friendly that the youngster would be welcomed at the Estadio Santiago Bernabeu.