Everton have rejected a £20 million bid from Chelsea for defender John Stones, sources have confirmed to ESPN FC.
Jose Mourinho wants to take the defender to Stamford Bridge, but Everton are adamant that he is not for sale.
Stones, signed from Barnsley by David Moyes for £3m in January 2013, started 23 of Everton's 38 league games last season, playing as Phil Jagielka's regular partner at centre-back.
He signed a five-year contract in 2014, a sign that manager Roberto Martinez sees him as part of the club's long-term future.
Chelsea captain John Terry said last month that he was "a big fan" of the 21-year-old centre-back, but Stones said at a fan event in Singapore on Thursday night that he is "very happy" at Goodison Park.
"My aim right now is try and nail down a regular spot in the Everton team and hopefully that will take care of playing for England," he added. "I have to keep learning from the likes of Phil Jagielka and keep progressing at the club."
Everton had been linked with a move for Manchester United centre-back Jonny Evans, but Martinez has denied that is the case.
Martinez also told reporters that he intends to "build a team of younger players who are proud to wear the Everton shirt."
Stones, who has four senior England caps, played for his country at the European Under-21 Championship in the Czech Republic in June.