The Millers’ boss has claimed that Ross Stewart will possess a threat in the second division now that Alex Neil’s side have earned promotion.
A 2-0 win in the League One play-off final ended the Black Cats’ four year stay in the third division.
Goals either side of half time from Elliot Embleton and Stewart clinched promotion for the club.
Rotherham also earned a place in next season’s Championship having come 2nd in the table behind Wigan Athletic.
But Warne believes that Stewart will give Sunderland the edge they need in order to stave off any relegation battle.
Speaking on EFL on Quest, the 49-year old shared his confidence that the striker will succeed in the second division.
“He’s a real handful,” said Warne, via Chronicle Live.
“He pinned the two centre halves back for Wycombe and it allowed the players around him to play. Sometimes his ability outweighs what he does in the game.
“They were so concerned with him as there were two on him, it allowed other players to get round him, pick up those pockets and potentially score more goals.
“He got his goal and he deserved that for his work rate.
“Shot through legs which I buzz off, I think it’s worth double, I love that and then celebrated with his fans at that end, that must of been the high point of his life and career.
“He’ll go on next year and he’ll be a threat in the Championship for defences, there is no disputing that.”
Quiz: Can you name which club Sunderland sold these 23 players to from the last decade?
Both clubs will be preparing for life in the second tier of the English football pyramid next season, with survival the ultimate aim.
Sunderland had a difficult campaign having dismissed Lee Johnson in January and only finishing 5th in the table.
But victories over Sheffield Wednesday and Wycombe earned an overdue promotion.
It is possible that Stewart would be preparing for Championship football this summer regardless of Sunderland’s play-off outcome.
The forward scored 24 times in the third tier and was one of the division’s standout players this season.
That Sunderland have earned promotion now gives him the opportunity to prove what he is capable of at this level.
If he can perform to the same standards, then Sunderland will no doubt be aiming for much higher than simply surviving.