The centre-back has been heavily linked with a move to the Scudetto holders this summer, although in the past few days Arsenal have emerged as contenders to sign the Greece defender following Thomas Vermaelen's move to Barcelona.
Former France international Karembeu, who is now Olympiakos' strategic advisor, says Manolas will not be sold for less than £8 million (€10m).
"Juventus are interested and have made a sound offer," the ex-Real Madrid midfielder told Tuttosport.
"They are not the only ones interested in him, though ... In the last few days interesting proposals have also arrived from England.
"We are in contact with Juve chief Giuseppe Marotta; we will see in the next few days if any meetings come from this.
"We are not willing to negotiate his sale for less than €10m. We have not set a deadline for clubs to bid but, if we receive the right offer, we are willing to sell him. Otherwise, we will keep him."
Karembeu conceded that the defender, 23, had approached him this month about leaving the club and is not surprised by interest in him following his performances as Greece reached the last 16 of the World Cup in Brazil this summer.
"Yes, Manolas confronted me recently," the World Cup winner added. "This is normal - he's a young guy and for the first time he is seeing his name linked with major European clubs.
"I'm not shocked by the attention he's getting. We were sure he would become a player with a lot of international interest in the transfer market, even more so after his great World Cup performances.
"Juventus are his number one choice but Kostas also has an emotional attachment here with Olympiakos.
"He has made a deal with the president that he will accept a transfer to whichever team meets the financial demands of the club, be that Juve or an English club."