The Italians lost in Greece to suffer their second straight defeat in the competition following their 1-0 loss at Atletico Madrid earlier this month. Juve have taken just three points from their opening three games and lie third in Group A, three points adrift of group leaders Atletico and Olympiacos.
“We simply were not able to make the most of our chances and that is why we go home with a defeat,” Allegri said in Gazzetta dello Sport. “Against teams like Olympiacos you cannot give away any chances and we gave them too many spaces in the opening half.
“We played badly in the first half but we reacted after the re-start and had opportunities to equalise and even with the match. I am disappointed with the result but I remain optimistic. I believe we will progress to the next round.”
Juve had gone into the encounter in Greece having dropped their first Serie A points of the season at the weekend in a 1-1 draw at bottom-side Sassuolo. That result saw Juve’s lead at the top of Serie A cut to one point.
“The game at Sassuolo and at Olympiacos have been the worst since I took over as coach,” Allegri said. “We nevertheless created in both games 15 goalscoring chances but the ball just wouldn’t go in.”
Juve host Olympiacos on November 4 before travelling to Sweden three weeks later to face Malmo, who are third in the group. The Italians end the group stages at home to Atletico on 9 December.