The 24-year-old joined the Magpies in the summer of 2014 from Nottingham Forest although he returned to the Championship club on loan for the 2014-15 season.
After officially linking up with Newcastle the following summer he has been a key figure in the heart of their defence.
He was instrumental in helping Newcastle win promotion back to the Premier League for the 2017-18 campaign and his performances have attracted interest from elsewhere.
Reports claim Premier League rivals West Ham have tabled a bid of £20 million, which would rise to £25 million, however the north-east side are understood to have rejected it out of hand.
Lascelles reported back for pre-season training on Friday and it is claimed Newcastle aren't willing to sell at any price.