The 54-year-old succeeds Ronald Koeman an the south coast club.
Belgium international played at St Mary's with new Spurs midfielder in the 2014-2015 season.
Juanmi moved to St Mary's Stadium from Malaga last summer
Koeman is expected to sign a new contract at St Mary's this summer.
Steven Davis' brace against Greece sent his country to a major tournament for the first time in 30 years.
The 28-year-old looks destined for Euro 2016 as England's second-choice goalkeeper.
Pochettino adds he's already identified where and how Spurs need to improve ahead of next season
Saints climb to the sixth position of the Premier League with one game remaining.
Tottenham need to hold onto second place despite their title disappointment.
Southampton signed the 22-year-old forward last summer from Malaga in a £5.5m deal.
Liverpool were also humbled by Swansea, who secured their Premier League status with victory.
Samir Nasri is ready to return to the squad for the trip to Southampton.
Schneiderlin admitts his disappointment at not being involved in the Premier League title race.
Sadio Mane is also available after his red card was rescinded.
The 23-year-old defender set to sign new three-year-deal at Anfield.
Liverpool visit Southampton on Sunday following 1-1 draw at Manchester United.
Meanwhile, Jay Rodriguez returned to action during the Under-21 victory over Middlesbrough.
Chelsea can move up to 10th with a win today.
Shaw has been out of action since September Champions League group stage game with PSV.
The England international is yet to play a game this season.
The Saints secured their fourth consecutive clean sheet at the Emirates Stadium.
The Gunners were held to a goalless draw at the Emirates Stadium by impressive Fraser Forster.