John Stones
Jose Mourinho has earmarked John Stones as their priority target this summer as a long term replacement for John Terry in the centre of Chelsea's defence Getty Images

Chelsea are concerned that both Manchester United and Manchester City are plotting a bid to sign John Stones from Everton, with the Blues having had two bids rejected for the England international, according to the Daily Mail.

Jose Mourinho has earmarked the defender as their priority target this summer as a long-term replacement for John Terry in the centre of Chelsea's defence. Terry has entered his mid-30s, which has prompted the manager to look at other viable options.

The Blues are likely to move in with a £30m ($47m) bid for the player before the end of the transfer window, but Everton have reportedly valued the player at £34m, the Mirror reported, and would sell to any club who reaches this valuation.

Both City and United have been recently linked with a move for a defender, with reports claiming that the Cityzens are closing in on a deal for Nicolas Otamendi from Valencia. United were interested in signing Sergio Ramos, but the defender has since pledged his future at Real Madrid, keeping Louis van Gaal to look at other options to strengthen his defence.

However, Chelsea are concerned as both clubs are in the race for signing the player and are awaiting Everton's take on the promising youngster. This summer, the Blues have made only two first team signings in the form of Radamel Falcao and Asmir Begovic, but are open to signing a couple of more players if the opportunity arises.

Chelsea have had a mediocre start this season, drawing 2-2 with Swansea City after Thibaut Courtois was sent off for a professional foul on Bafetimbi Gomis when the Blues were 2-1 up, giving away a penalty and allowing the Swans to come back into the game.

Meanwhile, champions Manchester City host the Blues in their second game at the Etihad, where a loss will spell major trouble for the visitors in their bid to challenge defend the title.