Ole Gunnar Solskjaer labelled Manchester United's defending in the 2-1 defeat by Istanbul Basaksehir as "unforgivable", but laughed off suggestions his job is under threat.
A shambolic first-half defensive display meant the Turkish side raced into a 2-0 lead, and despite Anthony Martial halving the deficit before the break, United could not muster up an equaliser.
With United 15th in the Premier League Solskjaer also recognised his side are struggling to find positives, with Everton next up at Goodison Park on Saturday.
"The performance wasn't good enough against a team that worked and ran," Solskjaer told BT Sport. "They hit us on the break a couple of times and scored two goals like you sometimes do in Europe when you don't defend well enough.
"The first one we forget about the man up top and that's unforgivable. The second one, we're not very well organised to counter-press and win the ball back when we're playing. So two tough goals to give away and then we didn't have enough to come back second half.
"We scored from a cross, a good goal by Anthony, and then you think 45 minutes to save something from the game but second half we threw everything at it but we couldn't break them down.
"It's not easy to be positive now. Of course it isn't when you've just lost the way we did. But these players, they're good players and we have a chance on Saturday morning to get going again."
However Solskjaer did see the funny side of a question in the post-match press conference when asked if he feared for his job after recent results.
"I decline to comment on such a thing," Solskjaer said. "Of course, it's early on and opinions are out there all the time. You've got to stay strong. I'm employed by the club to do a job and I do that to the best of my ability with my staff.
"We weren't good enough, the full game," Solskjaer added, again criticising his side for the opener, which saw Nemanja Matic leave Demba Ba free behind him, as Istanbul found him with a simple hoof up the pitch.
"You play a short corner and everyone forgets the players we're playing against. Demba Ba gets in behind us, there's a lack of communication and lack of decisions.
"You don't usually see those goals at this level, you shouldn't concede easy goals like this, you know how hard it is to create chances and create goals. And when you give easy and soft goals [away] like the ones here today it makes it a lot harder."
Analysis: If it's not one thing, it's another
Sky Sports' Gerard Brand
Over the past few games, Manchester United's midfield had been the focus of discussion. Why wasn't Donny van de Beek being used? How can Paul Pogba be shoe-horned into the team? Will the diamond work? Promptly followed by: why doesn't the diamond work?
But on Wednesday night, United's defensive frailties were all too obvious again, and their lack of creativity in the final third against a low block highlighted once more.
The opener, scored by Demba Ba, was schoolboy stuff. It's a goal you almost exclusively see deep into second-half stoppage time when a team is chasing the game, not in the 13th minute of a goalless Champions League tie.
The second, while less bizarre, was equally worrying, with United losing the ball and caught high up the pitch. Basaksehir, sitting deep themselves, were queueing up to score. These were positional errors you don't expect to see at any level.
And in attack, Anthony Martial and Marcus Rashford consistently ran into cul-de-sacs trying to find space in-behind a defence happy to sit back, a problem Solskjaer has experienced against stubborn sides throughout his time at Old Trafford.
Despite the focus being on the defence and attack, even the midfield can't escape criticism. Tempo was difficult to gain with both Juan Mata and Nemanja Matic in the XI, while Bruno Fernandes had his worst game in a United shirt.
Simply, United were beaten in every area of the pitch. Just a week on from the 5-0 win over RB Leipzig, this was a night to forget as this side once again flip-flop between the wonderful and the woeful.
Manchester United travel to Everton in the Premier League on Saturday at 12.30pm. Istanbul Basaksehir host Genclerbirligi in the Turkish Super Lig on Sunday at 1pm.