Sunderland were expected to up the ante for Souttar after seeing a £400,000 bid for the 17-year-old rejected during the summer.
The two clubs are understood to have been in contact ever since and have now reached an agreement over an initial £600,000 payment, plus a hefty sell-on clause for the centre-half.
Sunderland are the only club who have made a concrete bid for Souttar, who has made 14 first-team appearance since he was handed his debut last January.
Source: Sunderland-Mad
Source: FOOTYMAD
