Porto coach Sergio Conceicao is unsure if Pepe will make tonight's Champions League clash with Liverpool.
The veteran defender missed training on Monday.
Conceicao said: "The situation is not good. He has not trained today, we'll see tomorrow.
"He will be in doubt until the end. At the last minute. Obviously whether or not there is a big difference.
"Not that the others are less strong, but he is a player with great experience and in these matches it is essential to have men like this in such an important department."