Everton have completed the signing of teenage defender Mason Holgate from Barnsley for an undisclosed fee, understood to be an initial £1million.
Holgate, 18, has put pen to paper on a five-year deal, keeping him at Goodison Park until 2020.
But Everton have insisted Holgate has not been signed as a potential replacement for John Stones, who will not be sold to Chelsea, according to manager Roberto Martinez.
Martinez said: “I have said before the player (Stones) 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.
“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.”
England centre-back Stones has been the subject of two failed bids from Chelsea, the last worth £26million, but Jose Mourinho shows no signs of giving up his pursuit while Manchester United and Manchester City have also been linked with the 21-year-old.
Holgate is a product of the same Oakwell academy as Stones, who Everton signed from Barnsley for £3million in January 2013.
Since Holgate made his Sky Bet League One debut last December, comparisons have been made with the England international.
But Holgate has made only 22 first-team appearances for Barnsley and Martinez is keen to play those down.
“Mason, at 18, has already played 20 games in League One and that shows the potential he has,” Martinez added.
“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.
“Mason is a completely different type of player to John but in terms of personality and character they are very similar.”
Holgate had been linked with a move to Manchester United after spending time on trial with the club earlier in the summer, but an expected bid never materialised, while Bournemouth and Newcastle had also been interested.