USA international Paul Emerick has agreed a three-month deal with Ulster.
The 30-year-old, who has previously played for Newport Gwent Dragons and Parma, arrives at Ravenhill as cover for the injured Andrew Trimble.
Irish international Trimble is likely to be out of action until the end of October after suffering a finger injury while on tour with Ireland.
Ulster have also completed the signing of former Manly rugby league full-back Adam D'Arcy.
The Australia has been on trial at the club but has now agreed a one-year deal.