The Ireland flyer could line up against his old side for the first time when the side from Northern Ireland travel to Swansea this weekend.
And Tandy knows they will have to keep a close eye on the man still holds their try-scoring record over a season – 15 in 2009-10.
He said: “Tommy’s a good man and was a great character for the Ospreys to have. He left something behind at the region.
“When the boys came across him out in Ulster, for instance, you can see what an effect he had on the group. His scoring record is phenomenal and he has shown by winning all his caps with Ireland that he’s an outstanding international.”
Ospreys are without a win since halloween when they beat Connacht 26-11 at the Liberty Stadium. Ospreys will be hoping to get revenge on Ulster, who stripped them of their unbeaten league record when they claimed a 25-16 victory at the Kingspan Stadium last month.
Tandy’s men fell to another defeat in Ireland a week later when Leinster triumphed 18-12 at the Royal Dublin Showground. Munster knocked them off top-spot in the PRO12 following the loss, and Tandy is aware of Ulster’s threats across the pitch.
“They’re a well-balanced team with a good pack and good backs,” said Tandy.
“There’s quality across the board with people like Darren Cave, Ruan Pienaar, Tommy and Rory Best, while they have some good foreigners, including Nick Williams. We know it’s going to be a tough encounter but we also know if we want to be pushing for the top four we need to win at home.”
