The Leeds coach is normally extremely reluctant to point to injuries as a reason for defeat, pointing out in his pre-match press conference they were not the reason his side find themselves in a relegation battle.
Centre-back Pascal Struijk stepped into the position, but dropped back into defence when Diego Llorente came off at half-time. Adam Forshaw anchored the midfield in the second half.
Leeds's defending for the first two goals was poor, but Bielsa felt the absentees were telling.
"Evidently we've conceded a lot of goals," said Bielsa. "The amount of goals conceded is not linked to the individual skills defensively.
"It's difficult for us to prevent the opponent creating danger. To form a more compact block is not simple.
"The fundamental problems are with the recovery of the ball in the middle of the pitch.
"We had to be without Phillips, who is a defensive midfielder, after that without Koch and without Pascal, who is another defensive midfielder.
"In the second half we had to put Pascal back in the defensive line. Due to the absence of three players who can do that function, the composItion of the midfield doesn't have a defensive profile. That had an influence in the defensive behaviour of the team.
"We've conceded 50 goals in the league and I'm just commenting on the game today."
If the weaknesses of Leeds were on show, so were the strengths, showing great character to come from 2-0 down at half-time to equalise with goals from Rodrigo and substitute Raphinha which were just 24 seconds apart.
"To not fight would be worrying," said Bielsa. "To fight is a starting point but it's not the only thing.
"The game didn't become chaotic from my point of view. We stopped being in charge of the game and a product of not being in charge of the game, we lost the ball.
"In the moment of the two goals we missed a very clear chance to score at 3-2 and the response to that, they went down the other end and scored (through Fred).
"They missed very few chances, they were very efficient and we were less efficient and the difference comes through that.
"We had seven or eight chances to score, just like the opponent, but they scored a higher proportion."
Leeds were not given a concussion substitute to replace Koch, with television reporting the Whites had not asked soon enough.
"He had a cut in his head, and what excludes him or makes him come off is the cut," he explained. "So if the cut is the most significant thing, then the knock that he received, I acted in accordance with that."
Bielsa, though, claimed he would not have made a fourth change had it been available.
"No, in the second half our performance was better than in the first," he said. "I didn’t observe a player who would have deserved to come off the pitch. That doesn’t mean that having a fourth change isn’t something favourable."
Leeds remain five points above the Premier League relegation zone ahead of Wednesday's trip to Anfield.