The centre-half was on a yellow card as United were 2-1 down in the game against Istanbul Basaksehir.
Despite Solskjaer's change, which brought on Scott McTominay for Tuanzebe, United were unable to come back in the game.
Solskjaer told BT Sport: "Well it's a yellow card and we needed to go for it and gamble, to go forward. So the yellow made my decision."
The manager admitted he was despondent about the result and his team's performance.
He added: "The performance wasn't good enough against a team that ran and worked and caught us on the break.
"We didn't defend well enough. We threw everything at it but we couldn't break them down.
"It's set us back a lot. You get a reality check when you play a football game here. You don't just turn up and get three points in the Champions League. We played against lots of good individuals in a good team, well set up and organised. We weren't good enough.
"It's not easy to be positive, not when you play like this."