Stoke defender Shawcross left Old Trafford at the start of 2008 in a £1million deal.
But Ferguson has monitored his progress and nearly re-signed the 21-year-old defender during the summer.
Now, the Old Trafford boss will have to decide whether to move for Shawcross in the January window or wait until the end of the season.
And if misgivings about the performances of Ferdinand and Nemanja Vidic continue, Ferguson could be tempted to act sooner rather than later.
Shawcross would be eligible to feature in the Champions League knockout stages.
When Ferguson sold Shawcross, he insisted on a clause that means Stoke must give United first option on the player. A host of big clubs - including Liverpool - have shown a major interest in Shawcross, who is not without a chance of being called up for England's friendly against Brazil in Doha.
Should one of those clubs make a bid that Stoke find too hard to resist, United must be given the chance to match it.
Otherwise, Ferguson will have to make his own bid. It would be in the region of £8m - a figure that seems low but takes into account the significant sell-on clause that United also put in the original Shawcross deal.
Ferguson is sure to address the issues at the centre of his defence, and Shawcross has established himself as one of the Premier League's most reliable performers.
The feeling at Stoke is that it's not a matter of if Shawcross rejoins United . . . it's when.
he would make a very welcomed return. i foresee him and evans 5 years from now commanding the defence