The Argentine was furious after watching his side slump to a defeat in Switzerland that leaves Los Che with a mountain to climb ahead of next week's return at Mestalla
A first-half brace from Matias Delgado put the hosts two up at the break and although Valencia improved after the interval, Valentin Stocker's stoppage-time chip put the Swiss outfit in complete control of the tie heading into the second leg in Spain next week.
"I have no explanation of how we went out to play," Pizzi confessed. "I am ashamed of the way we played in the first half.
"I do not understand why we didn't play the first half as we did the second. At the break all we did was correct what is wrong because we did not do anything at all right in the first half."
In a clear warning to his players, Pizzi threatened to axe those who had let him down as well as demanding a significantly better showing in the home leg.
The Argentine added: "We are aware how difficult qualification will now be. I will try to find answers individually or from the whole the group that allows us to be closer to what was done in the second half rather than the first.
"If I cannot find the balance with these players, I'll go searching and modifying options with the squad I have. I do not want to be represented by this form of playing football.
"We must hold on to the fact of playing at home, although it is very difficult to reverse this result. We will do everything possible to show that we want to overcome the tie."