Zanetti faces eight months out with an Achilles injury suffered in defeat to Palermo.
"I am not a medic, but a lesion to the Achilles tendon does sound serious," said Stramaccioni.
Initial fears are that Zanetti could be out of action for eight months, which could end his career as he turns 40 in August.
"It's another heavy blow and one we really could've done without, because Zanetti's value to us is incredible. It's difficult to comment on a situation like this."