Ulster centre Paddy Wallace will miss the rest of the season with an ACL injury sustained in last Friday's match with Glasgow.
The 33-year-old requires surgery which will rule him out for the rest of the campaign.
Jackson was substituted early in the second half having filled in at fly-half for youngster Paddy Jackson, who was away with Ireland.
Ulster said in a statement that Wallace "will require surgery and a significant period of rehabilitation".
The injury means that Wallace fellow casualties joins winger Tommy Bowe and flanker Stephen Ferris on the sidelines as Ulster prepare for their Heineken Cup quarter-final with Saracens at the beginning of April.