Trimble dislocated his finger in Ireland's heavy defeat to the All Blacks in New Plymouth in June, but the fracture was only discovered when he returned to training with Ulster this week.

Now he will have to undergo an operation to repair the fracture dislocation to the finer on his left hand and is set to miss at least the first four rounds of matches in the newly expanded Magners League tournament.

It means the Belfast-based outfit will have to do without the services of their 25-year-old strike-force for the opening home game against the reigning champions, the Ospreys, as well as the games against Magners League new boys Aironi, Edinburgh and Connacht.

The injury could keep him sidelined for up to 12 weeks in the worst case scenario and will come as a major blow to Ulster coach Brian McLaughlin. Trimble has scored 20 tries in 71 Magners League appearances for Ulster.