Although the Claret and Blue don't realise the value of 22 year old, other clubs do, including Bolton, who may rival Blues in a bid.
Cahill is rated at £4 million by the Villans and it is understood that they won't negtiate on the price.
The central defender became a Holte hero after scoring in a 3-1 win at home to Blues two seasons ago and it was thought that he would go on to cement a place in the Villa first team for years to come. However, since the arrival of Martin O'Neill he has had little chance to shine.
The situation is very similar that of Liam Ridgewell before he made the move across the second city. He was limited in first team chances and decided to move in order to obtain regular football. Ridge is now captain of Blues but gave his old side a helping hand when scoring at the wrong or is that right end at St Andrews as Villa won 2-1.
If Cahill does join the Blues he could form a commandng partnership with Ridgewell, but many fans of the Claret and Blue will hope that doesn't materialise. If he is going to leave then we don't want him to follow Ridge in becoming another pantomime Villan.