Kalidou Koulibaly: Chelsea set to sign Senegal defender from Napoli on four-year deal

  By Sedara Oluwadara   Chelsea are set to sign Senegal defender Kalidou Koulibaly from Napoli on a four-year deal.   The 31-year-old flew to London on Wednesday to undergo a medical and finalise the move, before he joins Chelsea on their United States tour.     Chelsea are also close to bringing in Manchester