The 21-year-old striker enjoyed an impressive loan spell at the club under Nigel Pearson last season.
However, on his return to Sunderland, boss Steve Bruce ruled out any future move involving Waghorn - who scored 11 goals for City on their way to the Championship play-offs.
But with Bruce in desperate need of cash to bolster his squad to compete in the Premier League - Ghanaian World Cup star Asamoah Gyan is on top of the Sunderland manager's wish list - a £2million approach for Waghorn may just prove to be too tempting.
The summer transfer window comes to a close at 5pm on Tuesday and an eleventh hour move for Waghorn may just kick-start the Foxes' season.