The 17-year-old has attracted the attention of a number of Premier League clubs but the managerless North East outfit have jumped the queue with the first concrete bid.
United boss Jackie McNamara is uncertain of the youngster's future but is hopeful that he will yet remain north of the border, telling reporters: "The latest is that he is still a Dundee United player.
|12/1||Jozy Altidore is 12/1 with William Hill to score in a Sunderland win over Manchester United
"I think it is important now that we have that dialogue with John. If [joining Sunderland] is what he chooses to do then we will never stand in anybody's way but, if you are asking my opinion, then I think he would be best to stay here for the next couple of years and get a few games under his belt.
"It will be his decision. He has just turned 17, it is all about his development. He is part of our first-team squad at such a young age and it would be good for him to play 100 or 200 games first and get that experience."
Souttar looks set to play against Kilmarnock on Saturday, despite having a tour of Sunderland's training facilities the previous weekend, and McNamara hopes that the offer will give the defender an extra boost for the future.
"If anything, I think it will give him extra confidence," he added. "He's quite a level-headed young lad and he has a good family behind him. He won't be fazed by anything."