Chelsea are reportedly interested in signing Jan Oblak from Atletico Madrid this summer.
The Blues have already added striker Timo Werner and midfielder Hakim Ziyech to their squad, and are seemingly confident of sealing a deal for Bayer Leverkusen midfielder Kai Havertz.
But Chelsea's defensive problems this season have been well documented, and Blues boss Frank Lampard is thought to be keen on adding reinforcements at the back as well as further up the pitch.
Kepa Arrizabalaga was dropped earlier in the season before regaining his place after Willy Caballero replaced the Spaniard for several matches.
However, the £71.6million goalkeeper's form has continued to be inconsistent and The Mirror claim Chelsea are eyeing a move for Atletico stopper Oblak.
The Slovenian international is considered to be among the world's top goalkeepers and has played a key role in Atletico's strong defensive record in recent years.
If Oblak was to join Chelsea, Blues supporters will be looking forward to seeing the 27-year-old holding the shirt at his unveiling - but what squad numbers could the goalkeeper take at Stamford Bridge?
Since joining Atletico 2014, Oblak has worn the number 13 shirt, a squad number he also wore at previous club Rio Ave FC. However, the stopper did wear 41 at Benfica before he moved to Madrid.
At Chelsea, the incumbent no. 13 is Caballero, and the Argentinian only recently signed a one-year contract extension at the club.
The veteran keeper was due to become a free agent this summer, but will now remain in west London until the end of the 2020/21 season.
This means Oblak will only receive his favoured number if Caballero decides to relinquish his current shirt - or in the now unlikely event that he leaves.
Atletico Madrid manager Diego Simeone previously failed to issue a hands-off warning when asked about Oblak's future by Cadena SER .
Simeone said: "It is normal that they want a goalkeeper of the characteristics and value that Oblak has and it doesn’t surprise me because he is very good.
"For us, he is decisive, very important in the dressing room, he is our captain.
"Year after year he has managed to evolve in all the matches, from goalkeeper to his handling with the group, and hopefully he can continue with us.
"It is normal to always look for the best, and we have many who are very good, some previous seasons have left, others have stayed, and it is logical and normal for a footballer like Oblak to be loved by anyone.
"For us, he is our captain, an important player year after year and hopefully we can continue to count on his work, which is enormous for Atlético de Madrid."
