The Catalan giants have been rocked by the news that 32-year-old Ter Stegen could be sidelined for up to eight months and miss the rest of the season with an ACL injury sustained in the 5-1 La Liga win over Villarreal last weekend.
Barca have confirmed that Ter Stegen will undergo surgery after suffering a rupture in the patella tendon in his right knee and a further update on his condition will be released in due course.
The German's absence has forced Hansi Flick's side to delve into the free transfer market to recruit a short-term replacement, with Wojciech Szczesny set to come out of retirement and sign a one-year contact.
It is understood that Barcelona have also begun the process of drawing up a list of long-term goalkeeping targets who could either rival or replace Ter Stegen as the club's new number one from next season onwards.
Barca eyeing up future move for Costa?
According to Mundo Deportivo, Porto's Diogo Costa is among the goalkeepers that Barcelona have identified as a long-term target.
The report adds that the Portugal international is viewed as a 'very popular' choice by the club's hierarchy, including Portuguese sporting director Deco.
Barca are said to have followed Costa for some time and believe he has the ability to establish himself as a first-choice goalkeeper for the club that aspires to fight regularly for the Champions League.
It is understood that Barcelona are also admirers of Giorgi Mamardashvili, but he joined Liverpool for around £30m in the summer and has since returned to Valencia on loan for the current campaign.
Barca 'turned down' €12m Costa move in 2022
According to Radio Barcelona, Costa's agent Jorge Mendes offered the shot-stopper to Barcelona for just €12m two seasons ago, and although the deal was considered attractive by Barca, they ultimately opted against the move at the time.
Barca's current financial predicament could hinder their chances of luring a player of Costa's quality to Camp Nou, as the 25-year-old is valued in the region of €45m (£37.5m).
Porto are under no immediate pressure to cash in on Costa, who is under contract at the Estadio do Dragao until the summer of 2027.
Costa, who has previously been linked with Manchester City, Chelsea and Arsenal, has kept 68 clean sheets in 162 appearances for Porto across all competitions, including 14 shutouts in 33 Primeira Liga outings last season to win the Golden Glove.
Porto's No.99 has won a total of eight trophies with the club over the last five seasons, including two Primeira Liga titles and four Portuguese cups, while he has also been named Primeira Liga Goalkeeper of the Season on two occasions.