It means any future bids for the England defender can be rejected the Foxes should they maintain their stance of not wanting to sell him.
Maguire signed a five-year deal earlier this month following a summer of transfer speculation where Manchester United were unsuccessful with two bids for the 25-year-old, the biggest of those understood to be worth £60m.
Negotiations over an improved contract began when Maguire returned from the World Cup, with Leicester keen to reward the man described by manager Claude Puel as the “club’s best player”.
Sky Sports News understands the issue of a buy-out clause was one of the key sticking points, with the club adamant one would not be included in the new deal.
Maguire played every minute for Leicester in last season’s Premier League as they finished ninth, and featured in all seven of England’s World Cup games as they reached the World Cup semi-finals.
He has also been an ever-present for the Foxes in the league this campaign, picking up his third yellow card in five games during last Saturday’s loss at Bournemouth.