Chelsea are on alert after the agent of Porto defender Alvaro Pereira refused to rule out the possibility of his client leaving the club this month.
Chelsea tried to sign the full-back last summer, with then-manager Andre Villas-Boas failing in a bid to lure him away from his former club, and the Blues have continued to show interest in the Uruguay international as they look to bring in a new right-back this summer.
Porto last year had insisted they would not sell Pereira to Chelsea for less than than the value of his buy-out clause - believed to be set at around £26million.
It was later claimed that the Portuguese club refused to do business with the Blues in a bid to "get back" at the west London club for luring Villas-Boas, who is now in charge at Tottenham, to the Premier League.
Pereira recently admitted he is open to leaving Portugal during this summer's transfer window, and according to his agent, a move could happen.
"I spoke with Alvaro last week and he is calm," Flavio Perchmen told Antena 1.
"We are waiting to find out if there is any offer.
"We think everything will go well and that he can leave the club, but right now we do not have any concrete offer.
"Right now, he is 100 per cent at Porto. Last year, there was a 98 per cent chance of him leaving, but the remaining two per cent prevailed.
"Therefore, if someone makes an offer, we will look at what is best for the player and the club."
Pereira is also believed to be a target for Napoli.