The defender spent the night in Blackburn's Royal Infirmary where it was discovered he had broken two ribs and punctured a lung.
Boro boss Steve McClaren said "It's a massive blow for us because Ugo is one of our leaders. He is one of our top players."
It's the third serious injury inflicted on the Boro squad in recent weeks, following Joseph-Desire Job's fractured skull and George Boateng's cartlidge injury.