By Jamie Spencer Chelsea are believed to have agreed a deal with Aston Villa to sell left-back Ian Maatsen, who played in last month’s Champions League final while on loan at Borussia Dortmund. Maatsen moved to Germany on a short-term deal in January and was a key part of the Dortmund side that reached Wembley, where they were beaten by a clinical Real Madrid. But, despite proving himself at the highest level and Chelsea in need of a reliable left-back, the Dutchman is set for a permanent transfer to a Premier League rival. The upside is that the Blues will rake in a considerable fee for a pla…