The respected coach does not believe his side have a chance of progressing into the Champions League group stage, unless they put in a far better showing in the second leg
Dusan Basta put the Italians into the lead mid-way through the first half before Ismaily equalised for the hosts to set up a thrilling decider at the Stadio Friuli next week.
The 56-year-old is certain his side will fall at the final hurdle for the second season running if he does not witness a dramatic improvement on home soil.
"We are well aware that this performance will not be enough to get through. We won't get into the Champions League playing like that," Guidolin told reporters.
"We have done many great things in recent months, but to say we deserved to win tonight would be a lie.
"We must grow, as our fitness levels are not at their best. The second leg will be after we have played a Serie A match, so that could be important.
"This evening we made far too many mistakes and misplaced passes. If we weren't satisfied with the result, then we wouldn't be humble either. We are not Barcelona or Real Madrid."