Diego Costa could be confirmed as a £35million Chelsea signing by the end of this week. Atletico Madrid striker Costa has returned to training with Spain's national team ahead of the World Cup. That will clear the path for the west Londoners to complete a medical which has been held up by the hamstring injury which knocked him out of last month's European Cup Final loss to Real Madrid. Chelsea have already agreed terms, and the 25-year-old is keen to complete the move before the start of the World Cup.