Chelsea have made their first official approach to Borussia Dortmund to sign Christian Pulisic.

Sources in Germany say Chelsea spoke with Dortmund on Friday about acquiring the 20-year-old winger.

It is understood Chelsea made an offer for the USA star in an attempt to convince Dortmund to sell next month.

The German outfit want £70m for Pulisic, even though he has only 18 months left on his contract and is refusing to discuss an extension.

Chelsea’s bid is believed to be below the asking price, while Dortmund say he will see out the season with them.

Five players who Chelsea could replace Eden Hazard with this summer 6 show all Five players who Chelsea could replace Eden Hazard with this summer 1/6 Standard Sport runs you through five potential replacements for Eden Hazard… Getty Images 2/6 Thorgan Hazard Borussia Monchengladbach



Why not keep it in the family, eh? 25-year-old Thorgan may not have quite the mercurial talent of his older brother, but he would be a fine alternative should Chelsea be pushed for a replacement. AFP/Getty Images 3/6 Christian Pulisic Perhaps the US international was signed with this in mind?



Chelsea secured Pulisic’s services with a £57.5m move, but he has been loaned back to Borussia Dortmund for the rest of the season. He will join up with his Chelsea team-mates in the summer. Bongarts/Getty Images 4/6 Hirving Lozano PSV



The Mexican, nicknamed ‘Chucky’, is comfortable on either wing and is currently enjoying a fine season in Chelsea’s favourite breeding ground, the Eredivisie. REUTERS 5/6 Lorenzo Insigne Napoli



A natural choice with nearly 140 games played under the tutelage of Sarri, the Napoli forward appears and ideal fit to replace Hazard at Stamford Bridge. AFP/Getty Images 6/6 Leon Bailey Bayer Leverkusen



The Blues kept a keen eye on the winger over the summer while the future of Willian was up in the air following a fallout with Antonio Conte, but it may be the case that they turn to the Bayer Leverkusen star to replace an even bigger name. Bongarts/Getty Images 1/6 Standard Sport runs you through five potential replacements for Eden Hazard… Getty Images 2/6 Thorgan Hazard Borussia Monchengladbach



Why not keep it in the family, eh? 25-year-old Thorgan may not have quite the mercurial talent of his older brother, but he would be a fine alternative should Chelsea be pushed for a replacement. AFP/Getty Images 3/6 Christian Pulisic Perhaps the US international was signed with this in mind?



Chelsea secured Pulisic’s services with a £57.5m move, but he has been loaned back to Borussia Dortmund for the rest of the season. He will join up with his Chelsea team-mates in the summer. Bongarts/Getty Images 4/6 Hirving Lozano PSV



The Mexican, nicknamed ‘Chucky’, is comfortable on either wing and is currently enjoying a fine season in Chelsea’s favourite breeding ground, the Eredivisie. REUTERS 5/6 Lorenzo Insigne Napoli



A natural choice with nearly 140 games played under the tutelage of Sarri, the Napoli forward appears and ideal fit to replace Hazard at Stamford Bridge. AFP/Getty Images 6/6 Leon Bailey Bayer Leverkusen



The Blues kept a keen eye on the winger over the summer while the future of Willian was up in the air following a fallout with Antonio Conte, but it may be the case that they turn to the Bayer Leverkusen star to replace an even bigger name. Bongarts/Getty Images

The Blues have prioritised strengthening in wide areas, with Eden Hazard yet to agree a new deal and Pedro and Willian in their thirties.

Pulisic has been monitored by Chelsea for some time and he is understood to have held a meeting with Dortmund a few days before Chelsea got in contact on Friday.

Chelsea are not Pulisic’s first choice — he would rather go to Liverpool, where he can be reunited with former Dortmund coach Jurgen Klopp.

Standard Sport has learned Dortmund have already targeted Thorgan Hazard (below, left), who is the younger brother of Chelsea’s Eden, to replace Pulisic.

Chelsea sold Hazard to Borussia Monchengladbach for £5.9m in 2015 and as part of the sale they installed an option allowing them to match any bid a club make, so they have an option to re-sign the 25-year-old.

The clause puts Chelsea in a strong bargaining position with Dortmund, as they can say they will not make a move for Hazard in exchange for coming to an agreement over Pulisic.