Napoli president Aurelio De Laurentiis says talks with Swansea over signing Michu are "well under way" but that no agreement has been reached.
The Spain forward did not travel to the USA for Swansea's pre-season tour because of the talks.
It is understood the Serie A club would like Michu on loan, with the Swans thought to be keen on a permanent deal.
"Michu? Negotiations are well under way for months but there is still no agreement reached," said De Laurentiis.
Three other Spaniards, Pablo Hernandez, Jose Canas and Alejandro Pozuelo, are also absent from the trip to America.
Former Valencia winger Hernandez is approaching the last year of his contract, but midfielder Canas and striker Pozuelo are not thought to be in the plans of manager Garry Monk.
Michu joined Swansea from Rayo Vallecano for £2.2m during the summer of 2012 and was the club's top scorer with 22 goals in his first full season.
His performances saw him linked with big-money moves, but he extended his stay in south Wales by signing a four-year deal in January 2013.
The former Oviedo and Celta de Vigo player's second season with the Swans was marred by knee and ankle problems and he scored only two goals in 15 starts in the Premier League.
Before the club left for the States, Monk said he planned to hold talks with Michu and wanted the striker to stay.
"He scores goals and with that type of pedigree he's always going to attract interest and rumours," said Monk.
"If an offer goes in and it's the right offer and the player feels he wants to move on, then you have those discussions.
"We'll have a chat and see what's the best way forward but as far as I'm concerned he's a Swansea City player and I'm hoping to have him for next season."
Former Wales and Swansea winger Leighton James believes the time is right for his former club to sell Michu, even though he has two years remaining of his current contract.
"If he's going to go, then get it sorted," James told BBC Radio Wales Sport.
"Even before he was injured last season he was giving out the impression that he didn't want to be here.
"His price has dropped drastically through his poor form last season and his long-term injury.
"So you can't expect to command the same sort of fee that you could have done 12 months ago after he had such a good season.
"But it doesn't do the club, the players or the manager any good to have this hanging over their heads during pre-season."
Another Swansea player, Ben Davies, has been linked strongly with a move to Tottenham Hotspur, but the Wales full-back has travelled with the rest of the squad to America.