The 23-year-old sealed a season-long loan switch to the North-East from Liverpool on transfer deadline day.
Coates arrived at Anfield on the back of helping Uruguay to Copa America glory in 2011 and was subsequently named Best Young Player of the Tournament.
However, injuries have curtailed the defender's progress in recent years, but Poyet hopes that his compatriot can flourish during his time with the Black Cats.
"When Seb came to England I said that he had all the attributes to be a perfect centre-back, he has the size, the ability, the aggression and the commitment, but sometimes when you go to a club things change very quickly," he told reporters.
"That happened at Liverpool with the manager and then he got an injury so he slowly found himself out of the team, but it is a good challenge and we will help each other – we will help him to come back to the international level he was before and he will help us be competitive."
Coates could make his debut when Sunderland host Tottenham Hotspur on Saturday.