Porto have placed a 30million euros price tag on defender Jose Bosingwa, who is rumoured to be a target of Manchester United and Aston Villa.
Bosingwa has reportedly caught the eye of United manager Sir Alex Ferguson and Villa boss Martin O'Neill, who could both be keen to strengthen their squad in the January transfer window.
The 25-year-old impressed in Porto's UEFA Champions League performances this season as the Portuguese champions finished above Liverpool in Group A.
However, Porto insist they do not want Bosingwa to leave the Estadio do Dragao and have issued the 30m euros (£22m) hands off warning.
"Only if we arrive at this proposition would we be interested in studying the possible exit," a Porto spokesman told the Portuguese daily newspaper A Bola.
"We are calm because the defender enters into our plans and nobody has presented an offer to Porto for Bosingwa."