John Terry has been a mainstay in the Chelsea defence for 15 years, but at the age of 34, could Jose Mourinho be eyeing up his long term replacement.
According to Sky Sports, the Blues have had a £20 million bid for John Stones rejected by his current club Everton, as Mourinho looks to make additions to a defence that only conceded 32 goals last season.
Since joining the Toffees from Barnsley in 2013, Stones has become a vital part of Everton's defensive line-up, but the Merseyside club may struggle to hold onto the England international if Chelsea return with a more suitable offer.
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With Everton themselves trying to wrap up a deal for Manchester United defender, Jonny Evans, it may signal the end of Stones' career at Goodison Park, despite this rejected offer.
Despite ankle surgery that kept him out for a long period of the 2014-15 season, Stones returned to sure up an Everton side that were teetering on the edge of a relegation scrap and is widely regarded as the future of the national side's defence.
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Stones' signature would in no way signal the end for club captain Terry, who looked back to his best last season marshalling the backline as Chelsea charged towards Premier League glory.
If anything, it would put more pressure onto Terry's defensive partner, Gary Cahill, who was dropped at times last season for young Frenchman, Kourt Zouma, following below par performances in crucial games, such as the 5-3 defeat to Tottenham where he failed to deal with the physicality and movement of Harry Kane.
With Terry entering the so-called 'twilight' of his career, his performance levels have shown no sign of dropping as he continues to be the captain and leader that has dragged Chelsea forward throughout the Roman Abramovich era.
The former England captain still has a few years left in him and can take inspiration from Ryan Giggs, who played on at the top level until the age of 40, but at some point Chelsea have to think about ushering in the new generation in defence.
In Zouma, the Blues have one of the best young defenders in the world and he looks set to challenge Cahill for his spot in the starting 11 and it would come as no surprised to see him overtake the England international in the pecking order.
If the 21-year-old was to move to Stamford Bridge it would equip Chelsea with a young set of defenders ready to take over the mantle at any given time from two Englishman who shared the defence duties for the past three seasons.
Having signed a new five-year contract with Everton in August 2014 Stones will not come cheap for the champions, but if Mourinho has singled out the Englishman as his primary target then it seems more a question of when he will sign, rather than if he will sign.