By North-west correspondent Alex Stevens

John Stones can become “one of the greatest players England has ever seen”, according to his manager Roberto Martinez.

As revealed by Football Insider in November, Manchester United are closely monitoring Stones, while there is also interest from Chelsea, Manchester City, Barcelona and Real Madrid.

Everton insist Stones will not be sold this month and the club intend to offer the centre-back a new contract.

The 21-year-old has had an impressive season after Everton refused to sell to Chelsea despite a string of offers up to £35million and the player submitted a transfer request.

But Stones received some criticism for his display in Everton’s defeat to Swansea last weekend, with some claiming his reading of defensive situations requires considerable improvement.

Speaking at his media briefing on Tuesday ahead of the Merseyside club’s League Cup semi-final second leg showdown against Manchester City on Wednesday night, Martinez is convinced the youngster can become an all-time great.

“My take is what I always have with young players,” Martinez said. “John is 21 and has played 68 games in the Premier League. We will never assess until he plays 100 games.

“He’s still a young man and is in the right environment to develop. We accept criticism, but John Stones can become one of the greatest players England has ever seen.”