Both Premier League clubs are said to hold an interest in the Greek international defender, along with Serie A giants Juventus.
And in a recent interview with Italian publication Tuttosport that was brought to our attention by The Daily Express, former France midfielder Christian Karembeu - who now works as Olympiacos' strategic advisor - confirmed the Italian club had made an offer for Manolas and made explicitly clear of the club's expectations with regard to his price tag.
Willing to sell
"Juventus are interested and have made a sound offer. They are not the only ones interested in him, though ... In the last few days interesting proposals have also arrived from England," he said.
"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 (£8m). 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."
While Karembeu is obviously attempting to ensure that Manolas' suitors are aware that it will not be simple to lure the 23-year-old away from Karaiskakis Stadium, in truth €10 million is not a fee that the likes of Arsenal or indeed Manchester United would struggle to pay.
Gunners boss Arsene Wenger has suggested that he is still in the market for a new centre-back if the right target can be identified, with Thomas Vermaelen's decision to join Barcelona leaving only new recruit Calum Chambers as adequate centre-back cover for Laurent Koscielny and Per Mertesacker.
Manchester United are surprisingly yet to make any new centre-back signings so far this summer, despite the departures of Rio Ferdinand and Nemanaja Vidic seemingly leaving Louis van Gaal somewhat short on quality in that particular area.
Watch: The latest Manchester United transfer news
Even with Olympiacos willing to sell Manolas at the right price, Manchester United and Arsenal look as if they could face a considerable battle to sign the player, with Bayern Munich also said to be keeping tabs on him in addition to Juventus.
Bayern - who lost 2-0 to arch-rivals Borussia Dortmund in the German Super Cup on Wednesday evening - are believed to be in the market for a new defender and would surely also have no trouble producing the relatively low fee required to tempt the Greek champions into parting with one of their most-prized assets.
The opportunity to link-up with arguably the world's most revered manager in Pep Guardiola could potentially be difficult for Manolas to turn down, although it is not yet clear if he has a particular preference for any of the growing list of clubs that have been linked with his signature in recent days.