Andriy Shevchenko has been accused of diving for the penalty that put Ukraine into the last 16 of the World Cup.
Shevchenko scored from the spot to beat Tunisia 1-0 in Berlin on Friday but Tunisia defender Karim Haggui, who was penalised for fouling the £30million Chelsea striker, claims the decision was wrong.
He said: 'For the penalty, I didn't touch him - Shevchenko has been very clever. We are very disappointed because I think that is a pity for football.'
Tunisia coach Roger Lemerre also said there was 'huge bitterness' among the players.
He said: 'I will never throw the first stone towards referees. They are on the field to do their job and there is no changing their decisions, but I must admit the bitterness among the players is huge.
'When you have fought like that you have the impression your team has been beaten unjustly.'
Ukraine head coach Oleg Blokhin admitted his side need to raise their game to a higher level if they are to have any chance of making the quarter-finals.
The luck of the draw has certainly favoured Ukraine in their first World Cup - an easy group will be followed by a last-16 match against Switzerland, one of the weaker sides left in the competition.
However, the Swiss are the only team yet to concede a goal and Ukraine will need to perform better than in their final group match against Tunisia in Berlin yesterday if they are to progress.
Blokhin said: 'We have achieved our first ambition which was to make it to the round of 16 but now we have down that we cannot rest on our laurels.
'The players looked nervous against Tunisia and we made heavy weather of it and lost our discipline after they had a player sent off.
'We cannot afford to do that in our next game.
'It's the first time Ukraine have got to the tournament, and now we have qualified from the group but I want to go even further.'