The Argentine striker, who helped propel the Nerazzurri to Champions League victory in 2010, fell awkwardly after getting his studs trapped just seven minutes into Thursday night's Europa League clash.
Stramaccioni is distraught that his forward, 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," Stramaccioni told reporters after the match. "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 percent 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."
Two goals from Rodrigo Palacio mean Inter goes into the second leg of its Europa League tie with a commanding lead and gave some reason for cheer on a night marred by Milito's injury blow.
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