Leeds United forward Tyler Roberts was substituted on and off in midweek.
Roberts came on as a substitute for Leeds at half-time against West Bromwich Albion, but was taken off under 30 minutes later, as the Whites looked to defend their lead.
Bielsa’s decision proved to be the correct one, as Leeds held on and claimed a 1-0 victory over the Baggies in midweek.
But the Whites boss has admitted that he thinks Roberts is upset over the substitution, even though he hasn’t let on.
Bielsa said: “He shows a lot of generosity with me but he knows that my decision touched him and even he understood the situation but I know that this decision hurt him and it is difficult to overcome in a short time, this.
“What I can explain is that he made a mistake after the first half. I interpret one situation in the game. And that moment did not happen.
“I thought that if we were going to put one player more offensive we were going to be able to adapt to this moment. After the match it was more difficult than I thought and the player had to try to resolve the situation – it is not my high point and after I doesn’t not make the second decision there is going to be a second mistake. But if I remove the player, he is going to hurt.”
Roberts is still trying to make his way back into Leeds’ first-team, after missing the start of the season through injury.
The Welsh international was playing fairly regularly towards the back end of last term, but is being nursed back to full health now.
Roberts looks likely to be in Leeds’ squad again at the weekend, as they look to extend their lead at the top of the Championship.
The Whites are set to take on Millwall tomorrow, in what should be a very feisty affair.