The Manchester City midfielder, who scored a stunning solo goal in the previous game against France, was brought on in the 57th minute as the Three Lions conceded four late goals.
The decision was met with bemusement by many within the game, but Boothroyd maintains he made the right call on the night – declaring the 19-year-old was ‘dead tired’.
“No, I don’t [regret it] Maybe I didn’t clarify this last night as well as I could have done,” he told talkSPORT.
“After the France game the likes of Phil [Foden] and Ryan [Sessegnon] were absolutely out on their feet – they were dead tired.
“I thought they needed to recover properly and I chose to have a plan to wait until the game died down a bit against Romania and introduce the lads in the last 20/30 minutes of the game.
“As it turned out we managed to get right with Phil and he’s available for the next game, but unfortunately we didn’t it right with Ryan Sessegnon and he’s pulled a hamstring three minutes into it.”
He continued: “Do I want Phil Foden on the pitch all the time? Yeah, pretty much most of the time.
“But I’m not going to make him suffer with injury, when I think I can help manage him properly in terms of his recovery.