The short answer is three, although it would be fair to say that none of them created a lasting impression and even dyed-in-the-wool Gunners may be hard pressed to remember all three. The first of them, chronologically, was right-back Nelson Vivas, who was signed from FC Lugano and made his debut for Arsenal when replacing Patrick Viera after 84 minutes during a 0-0 draw with Liverpool at Anfield on August 22, 1998. Initially signed as cover for established full-backs Lee Dixon and Nigel Winterburn, Vivas went on to make 40 Premier League appearances for Arsenal, mainly as a substitute. Having spent the second half of the 1999/00 season on loan to Spanish club Celta Vigo, he was unable to force himslef into Arsène Wenger’s back four and subsequently left Arsenal to join Inter Milan at the end of the 2000/01 season.
Next up for the Gunners was striker Néstor Fabián Caballero, a.k.a Tyson, who moved to Highbury on loan from Paraguayan Primera División outfit Cerro Porteño on October 29, 1998. Caballero made his one and only Premier League appearance for Arsenal on November 29, 1998, replacing
Freddie Ljungberg after 74 minutes during a 1-1 draw with Middlebrough at Highbury. Arsenal opted against signing him permanently and, at the end of the 1998/99 season, he returned to his parent club.
Last, but by no means least, came goalkeeper Damián Emiliano Martínez – not to be confused with Uruguayan midfielder Emiliano Martínez Toranza – who had been registered as an Arsenal player since 2010, but did not make his Premier League debut until November 22, 2014. On that occasion, he replaced the injured Wojciech Szczęsny after 59 minutes during a 2-1 defeat by Manchester United at the Emirates Stadium. All told, Martinez would make 15 Premier League appearances for the Gunners, breaking into the first team in June, 2020, following injury to first-choice goalkeeper Bernd Leno, before being transferred to Aston Villa in September that year.