Roger Schmidt could not hide his irritation at Bayer Leverkusen's failure to beat BATE Borisov on Tuesday.
A shocking error from goalkeeper Bernd Leno allowed Mikhail Gordeichuk to open the scoring with the hosts' first attack of the match.
Javier Hernandez missed a great opportunity to equalise on the stroke of half-time as his run of scoring in seven consecutive matches came to an end in Belarus.
Admir Mehmedi's looping volley levelled the score in the second half, but the Bundesliga side could not find the winner their efforts perhaps deserved on the balance of play.
"It's very annoying that we didn't win," Schmidt told UEFA.com.
"The early BATE goal threw us out of rhythm. After that we needed half an hour to come back into the match. Afterwards we had enough chances to win the match, which would have been well deserved.
"They just had one shot and that was their goal. That's real pity."
Leverkusen midfielder Christoph Kramer rued Leverkusen's lack of a goal poacher, adding: "If we had a Thomas Muller today, he would have put the ball in the back of the net."
The draw sees both sides remain outside of the top two positions and means holders Barca qualified for the last 16 prior to their match with Roma.