"Officially, the best player is Kaka," Eusebio told uefa.com.
"However, I believe today that Cristiano is the best without any doubt.
"I have always said that he has everything it takes to become the best player in the world."
Providing he heeds Eusebio's advice to "keep his head in the right place" it appears there is no limit to his talent.
"I always believed that he would stay in Manchester," said Eusebio.
"Depending on his condition and whether his head is in the right place, I think he can get better, because with every year that passes he will gain experience and he'll know how to improve on the pitch.
"He must not forget that he will have to work a lot in terms of pace and ball control, and he is actually good in this respect.
"Therefore, the advice I always give him is that he needs to keep forging ahead in a straight line. Then he will definitely go a long way."