Doncaster added Reiss Cullen for the 2019/20 season after the scrum-half signed a two-year-deal.
The 22-year-old joined from Bristol Bears, where he made 10 appearances, three coming in the British & Irish Cup and scored two tries during his time at Ashton Gate.
Reiss also featured for Cardiff Blues and Cornish Pirates in the 2017/18 season after signing from Scottish semi-professional side Watsonians at the start of the campaign.
The scrum-half arrived at Bristol from Watsonians and was a big part of the first team in Edinburgh during his three years there. He helped the club regain promotion to the top flight in 2015/16 and played in every match in 2016/17 as the team stayed up in the Scottish Premiership.