Tottenham are linked to Manchester United's Chris Smalling.
England's Chris Smalling in action with Scotland's Leigh Griffiths
It would be a big sign that Pochettino is set on continuing to play three at the back, a formation he shifted to midway through last season.
Smalling is an England international who has high hopes of playing at World Cup 2018.
He has dropped down the Manchester United pecking order, but won't be leaving Old Trafford to play back-up in a crucial year.
Tottenham's defensive duo of Toby Alderweireld and Jan Vertonghen is the best in the Premier League, and Smalling would have trouble breaking up a partnership which is established for club and country.
When Spurs played three at the back last season, the third player at the back was rotated.
Tottenham's Jan Vertonghen and Toby Alderweireld during training
Ben Davies filled in, while Eric Dier had some mixed performances in the position, and Kevin Wimmer was another option.
None of the trio are particularly convincing, which is why Spurs are linked with making new defensive signings.
Another name linked is Swansea's Alfie Mawson, but he is in a different situation to Smalling.
Smalling will have a selection of offers, and won't choose Spurs in order to play even fewer games than he did at United last season.
Manchester United's Chris Smalling in action with Fenerbahce's Robin van Persie
Only the promise of regular football would convince him to join Tottenham this summer, and the only way they can do this is if Pochettino is determined to continue playing a 3-5-2 formation.
If Smalling signs, it will be an early indication this is exactly what the Argentine intends to do in 2017/18.
Chelsea's Diego Costa in action with Manchester United's Chris Smalling