"So numerous lads were playing their first 45 minutes of the season", said the England manager.
As many as nine changes are expected from the side which started the 2-1 Nations League defeat by Spain, with Eric Dier confirmed to captain a team set to feature the likes of Jack Butland, Ruben Loftus-Cheek, Fabian Delph, James Tarkowski and Danny Welbeck.
They're intelligent footballers, they should have a view of what's going on.
"Harry falls in the category in which we have several players where we have to watch how much they play", said the Three Lions boss. "He's had three days of little training, so half-an-hour was ideal to keep him ticking over".
The security provided by the presence of three central midfielders behind him enabled Shaqiri to roam wherever his little legs wished to carry him, and he popped up all over the pitch in the first half. "So I thought this is a good opportunity to do it".
"Before I got in the players were trying to sort things out", he continued.
"Before I got in there the players were trying to sort things out", he explained. We kept the ball better after half-time also.
He started all but one of England's games at the World Cup and is arguably the first name on the team sheet at his club. "I think for the teams that went towards the end of the World Cup it's a really hard period because so many players have missed pre-season and you're not really sure what physical condition they're in". Southgate admitted sympathy for the Croatians, who he believes are having similar difficulties to his own side after going so far at the World Cup in the summer.