4 center backs that could improve Manchester United's defence

#2 Toby Alderweireld

Toby is a cheap option

The most experienced and by far the cheapest alternative on the list, Toby Alderweireld is could leave Tottenham this season. With a release clause of just £25m, Alderweireld has attracted attention from several possible suitors.

A cheap option, Alderweireld has been one of the Premier League's top defenders over the past few seasons and helped Spurs significantly in their pursuit of Champions League football.

A key figure in Belgium's team for the past decade, the defender would bring much needed experience to a United squad that desperately lacks leaders.

A calm and composed figure, Alderweireld is one of the best passers in the league and does not dive into rash tackles. He provides a world class option at a very low price.

#1 Kalidou Koulibaly

Koulibaly is the club's number one target

United's number one defensive target and one of the best defenders in the world, Koulibaly could cost a world record fee for a defender. The Senegalese defender is worth every penny.

At 1.95m, Koulibaly is near unbeatable in the air. He has been key to Napoli's amazing style of play, creating attacks from deep inside his own with stunning vision. The only obstacle blocking the movie would be the mammoth size of the fee and United's failure to qualify for the Champions league.

At 27, he is at the prime of his career and Napoli would be determined to hold onto him.