Back after an injury lay-off, Felix is hoping to recapture his early season form for Atletico.
For his part, Del Piero has already seen enough, convinced the Portugal international can become the best in the world.
He said, "He's already among the biggest, you should not wait and you should not waste time. He has it all.
"The only advice I can give him is to honour his extraordinary talent by giving everything in each training, being maniacal. This will be irresistible. I repeat: he has everything to be a number one now."