Andrea Stramaccioni was distraught after Diego Milito's season ended when he suffered a serious knee injury in Inter's 2-0 win over Cluj.
The Inter striker fell awkwardly just seven minutes into Thursday's Europa League clash, suffering ligament damage to his left knee.
Stramaccioni lamented that the Argentine, who was stretchered off at San Siro in tears, looks set to miss the remainder of the campaign.
"Unfortunately, this injury rather ruined the night," the Inter coach told reporters.
"It is a lesion to the anterior cruciate ligament, damage to the collateral ligament and capsule. It is a terrible injury and totally new compared to the problems he had in the past.
"There's a one per cent chance of this happening, but it happened to Diego. We now just need to know when he'll have the operation.
"It's awful news, as we all care for him as a person as well as a player. I am personally very close to him and feel so sad right now."