South Africa international Arno Botha's move to Ulster has fallen through following a medical assessment, the Pro12 club has announced.
Botha signed a two-year deal in January and was due to move to Belfast at the end of the Bulls' Super Rugby campaign.
However, the 25-year-old flanker has suffered a series of injury setbacks and Ulster were informed there was an increased risk in the deal.
Botha sustained a knee injury playing in New Zealand in April.
Bryn Cunningham, Ulster's Operations Director, described their decision as unfortunate for the player and the club.
"We were looking forward to welcoming him to Kingspan Stadium. However, we have acted with the best interests of team performance in mind," Cunningham said.
"We have meticulous processes for player recruitment and, having commissioned an independent medical assessment in South Africa, it was recommended that the risk had increased following his most recent injury.
"This view was shared by our own medical team.
"Everyone associated with Ulster hopes that Arno will go on to have a long and successful career.
"Once this decision was reached, we compiled an extensive list of potential targets and we will announce a signing to bolster the forward pack in due course."