Belgium coach Robert Waseige believes his side failed to show Tunisia enough respect in the 1-1 draw on Monday.
Waseige was gracious in his praise for the African side but disappointed by his team's attitude.
He said: "I am not really happy because everybody probably felt that it would be easy
to play against Tunisia, but that was not true as we have seen.
"The Tunisians were quick, marked well and stuck to the job. They were technically stronger than us and their individual actions were a lot better than ours.
"We always have problems against smaller nations and Tunisia is a smaller nation. In the past Belgium has always played better when we have not been the favourites."
Marc Wilmots put Belgium ahead in the 13th minute but Raouf Bouzaine levelled with a wonderful free-kick just four minutes later.
The result leaves Belgium needing to beat Russia in their final group game to be sure of qualification to the knock out stages.
Waseige is only too aware of what is needed but is optimistic about his side's chances.
He said: "I have never stated this was an easy group for us. I believe it is very open as all the teams are very equal."
"Tunisia played very well today so maybe it will be easier for us in our last game against Russia.
"Perhaps the players will adapt to the final game better when they have to win."