Celtic duo Caldwell and Barry Robson were regarded as being two deals just about "in the bag" ... but Wigan could throw a spanner in the works.
The Premier League will obviously be tempting to Caldwell, who is not known to be strong on loyalty and very prone to jump ship should a better offer come his way.
He begged Sir Bobby Robson (in tears) to join Hibs when he was stuck in the Newcastle reserves ... but was quick to move to Celtic when they dangled a carrot.
He has said this week he would like to join Boro ... but he also told Newcastle boss Chris Hughton he would be tempted by a return to Tyneside.
Strachan originally took both Caldwell and Robson to Celtic Park. So he is hoping that his relationship with the duo will help to cement a deal.
Scottish newspapers are reporting that Celtic have accepted Boro’s combined offer of £1.6m for the duo.