Jan Vertonghen was critical of Belgium's performance following a surprise 2-0 defeat to Morocco, referencing things he "better not say".
The Red Devils would have become the second side to clinch their spot in the round of 16 with victory, but they were well short of their best, failing to create opportunities before succumbing to two late goals.
Regarded as the last chance for glory for Belgium's golden generation, Roberto Martinez's side have now lost seven of their last 19 matches across all competitions (W9, D3), as many defeats as they had suffered across their previous 74 games combined (W57, D10).
While Vertonghen feels Belgium were strong for the majority of the clash, he did not shy away from expressing his frustration at the manner in which the opening goal was conceded.
Abdelhamid Sabiri's free-kick to the near post eluded Thibaut Courtois in a carbon copy of a first-half set-piece where Belgium were saved by an offside flag against Romain Saiss.
"We didn't create much. I think we were good overall, we didn't give much away, just an identical goal twice," he told Sporza.
"Twice a resumption of play at the first post. That ball should never go in. The first time we are lucky, but the second time not any more.
"There are a lot of things going through my head that I better not say, or at least not outside [the dressing] rooms.
"It's very frustrating. The first game was not good, and we got away with it well. Not today. I don't think we created any chances."
Defeat to Croatia in the final Group F match on Thursday would result in an early exit from the competition, but Vertonghen believes his side still have the strength in the squad to progress.
"I had the feeling that we were in a good position. We didn't get into trouble. They have a lot of quality in the front. So did we, but with them it came out more," he added.
"After the first match, we thought it could only get better. We were hoping to qualify for the next round today.
"Now we have a difficult final game in which everything will be at stake. The quality in the group is certainly there."