Swansea City chairman Huw Jenkins believes that Liverpool and Arsenal target Michu is now worth more than £30million, reports the Daily Mail.
The 27-year-old attacking midfielder enjoyed a scintillating breakthrough season in the Premier League in 2012/13, following a £2.2million move from Rayo Vallecano last summer.
And, after carrying his impressive form into the start of the current campaign, Michu was this week rewarded with a first-ever call-up to the Spain national team.
Michael Laudrup intimated that the Spaniard was worth £30million last December, just four months into his first term in the English top-flight.
And, Jenkins now says that Michu's valuation has increased even further, after he was picked for the upcoming World Cup qualifiers against Belarus and Georgia.
"We've seen with Tottenham and Gareth Bale that every player has a price," said the Swans chief. "We are not in that bracket with Tottenham but they sold a top player. We are realistic about that side of things.
"I would say Michael was about right with his valuation of Michu if you look at the current market, but this call up enhances that further.
"We know we have a very talented player and naturally we want to keep him."
News of Michu's ever-increasing price-tag will come as a blow to long-term admirers Arsenal and Liverpool, who have both been credited with an interest in signing Michu, without ever making an official enquiry about his potential availability.
Gunners boss Arsene Wenger was linked with a bid to bring the former La Liga star to the Emirates Stadium in the summer, while Brendan Rodgers has also been monitoring the player's progress at the Liberty Stadium, with a view to attempting to lure him to Anfield.
Michu is currently under contract with Swansea until 2016, meaning the Welsh club will be under no obligation to sanction his sale unless Liverpool or Arsenal meet their valuation.