The Portuguese right-back had been an ever-present for Lille this season, starting all six Ligue 1 matches and the defeat to Real Betis on the club’s return to Europe’s top table last month.
However, Santos had to be stretchered off after just 17 minutes against Le Havre at the weekend as he was on the receiving end of a mis-timed tackle by Amir Richardson.
It has since been revealed that the 24-year-old has suffered “a complete rupture of the anterior cruciate ligament in his right knee, along with a meniscal tear” and is now facing a lengthy spell on the sidelines.
A statement reads:"Tiago has thus suffered a serious injury that will require a lengthy rehabilitation. Today, LOSC's absolute priority is naturally to support its player, a member of the LOSC family, through this difficult time.
"The entire Club, its management as well as the sports and medical staff are fully mobilised alongside Tiago - who had already faced a similar injury in 2024 - in order to provide him with all the necessary human, medical and psychological support.
Tiago Santos was stretchered off in Lille’s win over Le Havre
AFP/Getty
"Beyond the injury itself, the circumstances in which it occurred and the lack of sanction raise serious questions for the club.
"Even though the intervention of the Le Havre player was visible in real time, many cameras captured the scene from different angles, slow-motion replays were immediately broadcast, and VAR can intervene in the event of a clear error or a serious incident missed, including a possible direct exclusion, no sanction was issued, not even a warning."
In addition to Santos, Lille have arrived in north London without Ethan Mbappe - younger brother of Real Madrid superstar Kylian - due to suspension after his red card against Betis.
Hamza Igamane, formerly of Rangers, is also sidelined with a cruciate ligament injury sustained in January, though is thought to be nearing a return to action.
Giroud is set for a emotional reunion at the Emirates Stadium, eight years on from leaving Arsenal for Chelsea but it has been widely reported that he will start the game on the bench.
Lille squad in full
Goalkeepers: Ozer, Gill, Sajous
Defenders: Srdanovic, Ngoy, Alexsandro, Perraud, Nianzou, Verdonk, Cossier, Goffi
Midfielders: Bentaleb, Haraldsson, Kjaergaard, Mukau, Andre
Forwards: Bakwa, Giroud, Sahraoui, Ueda, Onal, Perrin, Diaoune