Chelsea will explore the possibility of signing the young Real Madrid centre-half Raphaël Varane after agreeing to sell David Luiz to Paris Saint-Germain for an initial fee of around £40m, a world record sum for a defender.

David Luiz, a £23.5m signing from Benfica in January 2011, has played 143 games for Chelsea and claimed the Champions League and Europa League while at the club but found himself something of a stop-gap at both centre-half and in defensive midfield last season. At 27, and with Barcelona and Bayern Munich also established as long-standing admirers, he represents a saleable asset as Chelsea seek to rejig their squad within Uefa’s financial fair play regulations. He has agreed a four-year deal with the French club, with an option for a further season.

The fee for the Brazilian could rise to as much as £50m with appearances and honours – an amount PSG, who are more bullish about maintaining their lavish spending of recent years, are prepared to pay – and that would grant José Mourinho leeway in the transfer market this summer to strengthen his own squad. The Spain forward Diego Costa is expected to join from Atlético Madrid for £31.8m, triggering the buyout clause in his contract at Vicente Calderón, while there is interest in securing a second striker, with Bayern’s Mario Mandzukic admired.

Chelsea are also seeking a left-back to replace the departing Ashley Cole, with Sevilla’s Alberto Moreno and Filipe Luís at Atlético tracked. Mourinho has cover at centre-half, where John Terry has signed on for a further season, Gary Cahill has excelled and Branislav Ivanovic can perform. The youngsters Tomas Kalas – who played in the wins at Liverpool and Cardiff towards the end of the season – and Kurt Zouma, signed mid-season from St-Etienne but retained by the French club for the rest of the campaign, will also seek first-team involvement, though Chelsea will still look into recruiting Varane.

The France international, 21, played regularly under Mourinho towards the end of his time at Real but, hampered by an injury to his right knee, has found his opportunities more limited at the Bernabéu this term. Yet he remains a player of immense promise and Chelsea will find out their chances of securing his services in the days ahead.

Mourinho expects Nemanja Matic to be his first-choice holding midfielder next season, which would have limited David Luiz’s chances of playing that role. In the end the fee offered by PSG has proved too enticing as the French club, conscious of Bayern and Barça’s interest in the player, met Chelsea’s valuation.

Officials from the Parisian club have travelled to South America and David Luiz is to undertake a medical at Brazil’s pre-World Cup training camp and the move is likely to be concluded over the weekend. But he will not be joined in Paris by his current his club-mates Eden Hazard, a long-term target for PSG’s owners, Qatari Sports Investments, or Oscar as Chelsea are intent on retaining both attacking midfielders. Another midfielder, Frank Lampard, is still expected to sign a new one-year contract at the club before England’s departure for the World Cup finals.

The five most expensive defenders before David Luiz

David Luiz’s impending move to PSG could be worth up to £50m and would make him the world’s most expensive defender. But a big price tag does not guarantee success, just ask Fábio Coentrão. Doug Revolta takes a look at the five most expensive defenders in history.

1) Thiago Silva: Milan to PSG, £35.5m, 2012 The centre-back enjoyed three successful seasons with Milan before a big-money move beckoned to the French giants who took Zlatan Ibrahimovic in the same move. Silva has since become captain for PSG and the Brazil national side, claiming two Ligue 1 titles and the French League Cup to become widely thought of as one of the world’s best defenders, not just the most expensive.

2) Rio Ferdinand: Leeds United to Manchester United, £33.1m, 2002 A string of impressive performances at the World Cup with England in 2002 prompted United to make Ferdinand the most expensive British player in history. Ferdinand went straight into United’s defence and remained a lynchpin at the back throughout his time at Old Trafford, forming a formidable partnership with Nemanja Vidic after the Serbian joined in 2006. Ferdinand made over 400 appearances for the Red Devils and departs the club this summer after 12 years of service.

3) Marquinhos: Roma to PSG, £27m, 2013 Marquinhos joined Roma in the summer of 2012 for just £3.2m from Corinthians but a promising debut season in Serie A saw PSG pay £27m for the then 19-year-old who had just 26 senior appearances with Roma to his name. The defender has not been a permanent fixture at his new club this season however, and has often found himself making appearances from the bench. The Brazilian has only one international cap and failed to make Luiz Felipe Scolari’s World Cup squad.

4) Fábio Coentrão: Benfica to Real Madrid, £27m, 2011 José Mourinho met Coentrão’s buy-out clause and brought the left-back to Real Madrid off the back of his strong performances for Benfica. The defender signed a six-year contract with the Spanish outfit but has been a bit-part player during his three seasons in La Liga, often played out of his favoured position. Marcelo has remained Real’s first-choice left-back and Coentrão looked set for a deadline-day move to Manchester United last summer, only for the move to collapse at the eleventh hour. He continues to be linked with a move away.

5) Pepe: Porto to Real Madrid, £25m, 2007 After establishing himself as one of the top defenders in the Portuguese league, Pepe signed for Real Madrid in 2007 on a five-year contract. Barring an injury-stricken campaign in his second season in Spain, Pepe has been an ever-present for club and country since the move and has formed notable defensive partnerships over the years with Ricardo Carvalho and Sergio Ramos. The Portuguese player’s fiery temperament on the pitch has seen him involved in numerous controversial incidents, mostly involving Barcelona, and he has often felt the wrath of Real’s fans as a result.