Chelsea have reportedly been given a boost in their attempts to make defensive reinforcements this summer. Napoli defender Kalidou Koulibaly could be on his way to Stamford Bridge this summer.The 30-year-old has been one of Europe's most sought after defenders over the years for his impressive performances in the Napoli defense. Kouliably has made 314 appearances for the Naples side since joining from Belgian side Genk in 2014.Chelsea are in need of defensive reinforcements with Antonio Rudiger on his way to Real Madrid, as per transfer expert Fabrizio Romano. Andreas Christensen is also heading out of Stamford Bridge with a move to Barcelona agreed, as per AS.Both players' contracts expire in the summer and will therefore make their respective moves as free agents.Italian outlet AreaNapoli.it (via Football London) reports that the Blues have been given a proposal of £30 million to sign Koulibaly.kemboi@Cfc_KemboiKalidou Koulibaly Pocketing Your Favourite Players : This is why everyone wants a piece of him : 58371Kalidou Koulibaly Pocketing Your Favourite Players : This is why everyone wants a piece of him : 👇 https://t.co/Z34Cq8FdemThe Senegalese defender could be an astute replacement for both Rudiger and Christensen, with Thomas Tuchel in desperate need of defensive signings.Koulibaly is reportedly not pushing for a move but would be open to leaving should the opportunity arise.Another name being touted for Tuchel is RB Leipzig defender Joško Gvardiol. The 20-year-old has had a fine season for the Bundesliga side and can play both as a centre-back and left-back.Gvardiol has made 45 appearances this season in all competitions, scoring two goals and contributing three assists.Goal reports that the Croatian is a top priority for Chelsea this summer as they look ahead to a vital summer of dealing with defensive departures.Marcos Alonso eyes Chelsea exit amid Barcelona interestThe Spaniard reportedly wants to return to SpainChelsea left-back Marcos Alonso is reportedly looking to leave the club at the end of the season. According to transfer expert Fabrizio Romano, the Spanish defender is keen on a move to Barcelona.Barca reportedly have the left-back in their sights and Chelsea are open to selling but negotiations have not advanced at this juncture.Fabrizio Romano@FabrizioRomanoMarcos Alonso’s priority will be to leave Premier League this summer. The plan is clear and Barcelona have his name into the list, contacts ongoing #CFCAlonso would like to come back to Spain. Chelsea are open to sell but still nothing advanced due to current club situation.235091699Marcos Alonso’s priority will be to leave Premier League this summer. The plan is clear and Barcelona have his name into the list, contacts ongoing 🇪🇸 #CFCAlonso would like to come back to Spain. Chelsea are open to sell but still nothing advanced due to current club situation.Alonso, however, looks likely to be yet another defensive departure from Stamford Bridge, with Tuchel needing to make a huge number of changes to his backline.Alonso has filled in for the injured Ben Chillwell this season since November. He has made 42 appearances across all competitions, scoring four goals and contributing five assists.One defender that will remain at the club, however, is club-captain Cesar Azpilicueta. The Spaniard signed a new one-year extension last month despite reported interest from Barca.