It is a bitter blow for Wallace who now faces a race against time to be fully fit for Ireland's Six Nations assault.
However, Ulster coach Brian McLaughlin isn't worrying, adamant his squad has adequate strength in depth to cope with Wallace's absence.
He said: "To lose Paddy is a blow. After the World Cup he came back itching to play and it's very unfortunate for him.
"But in Nevin Spence we have an able replacement and we have no doubts he a can do an excellent job for us.
"We are very fortunate to have a lot of depth in that area with Ian Whitten and also Luke Marshall who is making his way back from injury."