Benfica sports chief Rui Costa says Axel Witsel has the ability to play for Europe's biggest clubs.
Rui Costa told Calciomercato.it: "He's one of the few young men of a high level ready to compete at a top club, although I hope he can continue with us for a long time.
"In the event of his sale, I hope he will move to a club that allows him to continue on his development path.
"We are proud of having come upon him before other clubs of a high level. Whoever will take him away from Benfica will certainly have to put in place a great investment."