Former Atletico Madrid forward Adrian Lopez has joined Villarreal on a season-long loan from Porto.
The 27-year-old, who won both the Primera Division and Europa League with Atletico, moved to Portugal last summer but failed to make a real impression for the Dragoes, scoring his solitary goal in a 6-0 Champions League victory over BATE Borisov in September.
The two-time Spain international linked up with his new teammates in a training session on Monday afternoon.
Chelsea face "not an easy draw at all" after they were placed in a Champions League group with Porto, Dynamo Kiev and Maccabi Tel Aviv, former Blues goalkeeper Carlo Cudicini says.
Manager Jose Mourinho is intimately familiar with Porto, having led them to the European title in 2004.
The Blues managed to avoid the elite Madrid clubs that were in Pot 2, but Cudicini, who attended the draw in his role as global ambassador for Chelsea, insisted that Porto will be every bit as difficult.