Roberto Martinez: Chelsea target John Stones is not for sale despite Everton signing Mason Holgate

Roberto Martinez has insisted Chelsea target John Stones will not leave Everton during the current transfer window, with the manager playing down suggestions that the club have signed Barnsley defender Mason Holgate to replace the England international.

Stones's future at Goodison Park has been under scrutiny in recent times amid speculations linking with Manchester United and, more noisily, Chelsea.

Jose Mourinho has reportedly earmarked the defender as his fifth signing of the summer to follow the arrivals of Radamel Falcao, Asmir Begovic and young duo Nathan and Danilo Pantic – with Brazilian starlet Kenedy expected to join them should he secure a work permit.

Nevertheless, following the departure of Filipe Luis to Atletico Madrid, the Blues have also been heavily linked with left-back Abdul Rahman Baba as the Portuguese boss has only five established first-team defenders in his ranks: Cesar Azpilicueta, Branislav Ivanovic, John Terry, Gary Cahill and Kurt Zouma.

But the Daily Mail recently reported that Everton were ready to turn down a £30m ($47m) bid from Stamford Bridge to secure the services of the young centre-back – having already rejected their two previous offers worth £20m and £26m.

Martinez has now confirmed that no matter the bid offered the club are determined to hang on to one of their key players.

"I have said before the player is not for sale and that is the end of it. Our situation has been very clear from the beginning. We are not a selling club who will lose our best performers," the boss said as quoted by The Guardian.

"His performance at the weekend was very strong and for a young man to come up with that leadership is a real sign of what he is as a footballer. He is very important player for us and we are looking forward to seeing the best of John over the next few seasons, not just the next few weeks."

The arrival of 18-yeas-old Holgate from Stones' former club for a reported £1m looked set to reopen speculations over Stones departure from Goodison Park.

Martinez, however, has played down that gossip after claiming that both deals are not related as Holgate is a signing for the future.

"Mason, at 18, has already played 20 games in League One and that shows the potential he has. We seem to have agreed terms with Barnsley and he will be a phenomenal young prospect coming into that golden generation we feel we have at the club and he will be a good one for the future," the manager added.

"Mason is a completely different type of player to John but in terms of personality and character they are very similar. "