Tim Boys will complete his short-term contract with Ulster without playing a game after being ruled out for the rest of the season because of a toe injury.
The 34-year-old from New Zealand has yet to make an appearance since signing in January, with the flanker's contract expiring at the end of the campaign.
Boys suffered a tendon injury in training last week and underwent surgery on Wednesday.
Lock Robbie Diack is set to return from injury against the Dragons on Sunday.
Diack has recovered from a back injury that has kept him sidelined for the past fortnight.
Paddy Jackson could make his comeback from a dislocated elbow against Cardiff Blues on 27 March, with the fly-half set to resume training on Tuesday.
Prop Wiehahn Herbst suffered cramp in a hamstring during Friday night's win over the Scarlets but he will be available for the Dragons game in Wales.
Ulster team manager Bryn Cunningham is disappointed by the absence of Boys for the remainder of the campaign.
He said: "It is particularly frustrating for all involved when they get through the initial bedding in period, become accustomed to the squad and the calling structures and are ready to integrate into the matchday 23, only to get injured that week.
"For this to happen to both Ronald Raaymakers, earlier in the season, and now Tim is exceptionally unfortunate."