The 31-year-old flanker signed from New Zealand's Southland Stags on a short-term loan deal in January in a bid to help solve the Irish province's injury crisis.
But while the Kiwi was preparing to make his debut for the club he suffered a tendon injury to a toe during training and has since undergone surgery which has ruled him out for the rest of the season.
And Ulster team manager Bryn Cunningham concedes the fact that Boys had not even made an appearance for the club makes this an even bigger blow to take.
"It is disappointing for both the province and the individual when a player is brought in as cover and sustains an injury that sidelines him for the duration of his short-term contract," Cunningham admitted.
"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."
Ulster currently lie third in the GUINNESS PRO12 standings but have struggled under the weight of injury losses this season with key players like Chris Henry ruled out with long-term problems.
And Boys is not the first Ulster short-termer to suffer an injury before appearing for the club with fellow Kiwi Ronald Raaymakers another player brought in who never featured for the senior side.
"For this to happen to both Ronald Raaymakers, earlier in the season, and now Tim is exceptionally unfortunate," Cunningham added.
Elsewhere Ulster have been boosted by the news that Paddy Jackson looks set to return in the club's PRO12 match against Cardiff Blues later this month.
The 23-year-old fly-half has been struggling with an elbow injury which has ruled him out since January but is expected to return to training today.
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