The Wallaby flyer received a head injury during Ulster's eight-try Celtic League walloping of Caerphilly at the weekend.

Also doubtful for selection is back-row forward Tony McWhirter who picked up a dead leg and was replaced at half-time by flanker Neil Best.

But while McWhirter is still hopeful of being fit for the opening Pool 6 test against Northampton at Franklin's Gardens on Sunday, Constable is already resigned to missing two games.

''It is disappointing to miss the games against Northampton and Cardiff,'' said Constable, who has gained the confidence of coach Alan Solomons this season.

''I don't really remember what happened.

''I can recall running onto the pitch for the match and making a run before I was tackled.

''The next thing I remembered was that it was half-time.''

Constable hopes to be ready for action when Ulster take on Llanelli in the final Celtic League match which will decide who will fill the final place in Pool A.

Ulster, meanwhile, are due to announce their team to face Northampton on Wednesday.