Tottenham Hotspur are going to have to bolster their squad with some real strength in depth as they tackle Champions League football next season.

side earned themselves a spot in next season's elite European club competition by making it through 15 matches to eventually win the Europa League in Bilbao. However, they struggled with injuries throughout the season and slumped to a 17th-place finish in the Premier League table, showing that the squad must be improved hugely to deal with the arrival of Champions League football on top of the domestic campaign.

football.london has taken a look through the squad to see what departments need work, including who could leave and where players need to come in. In this edition, let's look at the defence and what technical director Johan Lange will be trying to achieve.

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With the goalkeepers set for the foreseeable with Guglielmo Vicario, Antonin Kinsky and Brandon Austin tied down to long-term contracts and Josh Keeley and Luca Gunter high quality young stoppers, the first area that needs at least one new addition is in the full-back department.

, Destiny Udogie and the versatile Djed Spence look set for next season, barring any unexpected huge bids for their services over the summer, with all three having plenty of time left on their contracts. Archie Gray can also play in both full-back roles if required but Tottenham will want to use the teenager in his more natural central midfield role.

On the left, Sergio Reguilon has departed N17 after his contract came to a close. With the first team's longest serving player Ben Davies there has been plenty of talk about the option to extend his contract by another year, but nothing concrete on that actually happening yet. Leeds United are believed to have interest in reuniting the Welshman with his compatriot Joe Rodon at Elland Road and Spurs could well take up that option to ensure they get a fee for the long-serving defender.

It's likely that Spurs will look to sign another full-back regardless, likely to be one comfortable on the left to ensure balanced back-up to Udogie there, even if Spence can play that role well.

When it comes to centre-backs, Tottenham will go into this coming season with plenty of them on the books yet still potentially need another top quality one.

At this moment the north London outfit have , Micky van de Ven, Kevin Danso, Radu Dragusin - once he returns from his cruciate ligament injury - and Davies - if his option is taken up and he sticks around - as well as the incoming Luka Vuskovic and the returning Ashley Phillips and Alfie Dorrington.

Romero is the one where the biggest transfer doubts lie. He has been linked heavily with a move to Atletico Madrid and admitted he wants to play in La Liga at some point. Spurs can offer him Champions League football next season though and will expect a hefty fee if clubs do come in for the Argentine, who has two years left on his contract.

Tottenham will look again at the availability of , a long-time target at Crystal Palace who they made an approach for in January. The England defender has only a year left on his contract at Selhurst Park so will be a man in demand, but again Spurs can offer Champions League football. They're a far more attractive prospect than they were a fortnight ago, let alone five months ago.

Much will depend on whether Guehi would be guaranteed to start each week as he would elsewhere and Spurs will have a list of centre-backs to turn to. The issue of course is who the head coach will be and how that affects matters.

Tottenham have also been linked with Everton's Jarrad Branthwaite but the 22-year-old will cost a hefty sum to prise away from the Toffees.

If Davies were to leave this summer after 11 years at the club then Spurs might look for another versatile defender who can play both as a centre-back and full-back.

The teenage Vuskovic will be expecting a decent amount of game time as the season wears on and Spurs will have promised him a healthy amount of minutes when they saw off competition from Europe's top teams to sign the big Croatian. With four competitions and a packed schedule there should be opportunities.

For Phillips and Dorrington, much will depend on who is in charge because Postecoglou has not appeared to be sold on either as first team regulars as of yet, although their loans at Stoke and Aberdeen have helped developed their game this season.

There are plenty of decisions to be made in Tottenham's defensive ranks in the months ahead before the main summer window closes.