Maguire opted for a move to Leicester City rather than Spurs because he felt more game time would be granted at the King Power Stadium. As a result of this, manager Mauricio Pochettino is still interested in another centre-back in this summer's transfer window.
Smalling out of favour at United?
Smalling has been in and out of the United team last season due to injury and other competition at Old Trafford with the likes of Eric Bailly, Marcos Rojo and Daley Blind all featuring more times.
José Mourinho has added Victor Lindelof to his squad after the Sweden defender moved from Benfica earlier this month, adding more doubt to Smalling's United future.
The England international was signed from Fulham in 2011 and has made almost 250 appearances for United claiming a number of honours at the club. In his time in Manchester, Smalling has won two Premier League trophies, one FA Cup, one League Cup, three Community Shield's and more recently one Europa League.
Spurs look to bolster defence
Pochettino is interested in finding another centre-half to support current defenders Toby Alderweireld and Jan Vertonghen as the North London club attempt to go one further this season by claiming the Premier League title.
As well as this, they will also compete in this season's UEFA Champions League and will look to improve on last year's campaign where they failed to make it out of the group stages.
A deal this summer could be agreed between the two clubs for Smalling, which could involve midfielder Eric Dier who has already been linked with a move to United as they chase a centre midfielder for the new season.
Spurs are due to play their home games at Wembley Stadium for this campaign to allow developments at their new stadium to be completed for the 2018/19 season.