Christensen signed a four-year contract with La Liga club Barcelona on a free transfer with a €500 million buyout clause.
Christensen played for Chelsea U19 in the 2014-15 UEFA Youth League final against Shakhtar Donetsk in Switzerland, which the Blues won 3-2.
New York Red Bulls will host Barcelona in a pre-season friendly at the Red Bull Arena on Sunday.
Chelsea boss Thomas Tuchel believes defender Cesar Azpilicueta will extend his stay at Stamford Bridge.
Chelsea defender Antonio Rudiger is set to become a free agent at the end of the season and Barcelona are interested in him.
Barcelona president Joan Laporta has claimed the club wants to sign four players in the summer.
With new ownership coming in, it is unclear how much money will be available to spend in the transfer window.
James was also impressive in the weekend win over Burnley at Turf Moor where he registered a goal and an assist in a convincing 4-0 win.
According to Italian journalist Fabrizio Romano, Barcelona have offered a new five-year contract to sign Chelsea defender Andreas Christensen.
Chelsea thrashed Chesterfield 5-1 in the FA Cup fixture at Stamford Bridge on Saturday.