Liam Moore got the nod to start for England in their European under-21 Championship opener in place of injured centre-back John Stones.
Everton defender Stones had received a concussion in training after colliding with a teammate just 48 hours ahead of the fixture.
Leicester City centre-back Moore was hoping to seize on the opportunity, but cannot have been happy with the way the game panned out as the side suffered a 1-0 loss.
He struggled to get to impose himself on the Portuguese attack, and managed only to record a single tackle and interception each.
Moore did manage to block three goal bound shots, and made eight clearances. He nearly had a calamity early on after diverting the ball towards his own goal, which was impressively saved by Jack Butland.
The youngster was preferred by Southgate over Arsenal defender Calum Chambers who was left on the bench, and Tottenham's Eric Dier who ruled himself out of the squad after being told by the manager he would be used as a right-back rather than centrally.
Moore's partner in central defence was Middlesbrough's Ben Gibson, who himself made nine clearances and two tackles, but like Moore was put under real pressure by the Portuguese front line.
With Stones likely to return for England's next match against Sweden, one of the duo will move to the bench. Moore, who was at times positionally suspect, could be the front runner.
The defender, reported by the Yorkshire Evening Post to be a loan target for Leeds United, made only 11 Premier League appearances for Leicester last season.