Kevin Thomson insists 'schoolboy' football cost Rangers a victory against Stuttgart in the Champions League on Tuesday night.
The Bundesliga champions headed into the match at the Gottlieb-Daimler Stadion without a single point from the campaign.
But they ran out 3-2 winners after Ciprian Marica snatched a late goal to send Walter Smith's men back to Glasgow empty-handed.
Rangers now need at least a draw against Lyon in their final match to progress to the knockout stages.
'We'd have taken the position we're now in before the group games started, because we're close to making it to the last 16,' said Thomson.
'But we conceded sloppy goals here, the first one especially. I, Barry (Ferguson) and Charlie (Adam) switched off a little bit - which is schoolboy stuff.
'That's bitterly disappointing, especially because it came deep into injury time in the first half.
'We're all disappointed, because we felt the three points were there for the taking.
'It's never nice getting beaten at any time - but especially when you feel we could have won or got at least a point.
'We just felt from a tactical point of view we weren't quite as good as we'd have expected to be.'
Thomson has no doubts nonetheless about Rangers' ability to battle back.
'I think we've got that character in the team,' he said.
'We've got a group full of winners, with everyone in the dressing room striving for success at this club.
'We're all working hard as individuals and as a team, doing everything the manager tells us to do.'
Thomson insists there is no reason why Rangers cannot complete the job on December 12.
'We've got to be confident going into that game,' he said.
'It'll be a massive occasion for the club and all the boys. Everyone is already looking forward to that one.
'It would be a fantastic achievement to go through, but we're still faced with one more hurdle.
'It's a big hurdle to jump, and we'll need to be at the top of our game. That's the only way we'll progress into the next round. We beat them in France - but they're a fantastic side who will make it difficult.
'A draw is no good to them now, so we hope we'll get the result we feel we deserve from this campaign.'
Adam - who bagged the opener against Stuttgart - is also confident.
'On the night, the three goals we lost were disappointing - and now we have to look forward to the next game,' he said.
'It's a cup final for us at home against Lyon. I know that if we had drawn the match it wouldn't have changed what we have to do in the last game - but it is still disappointing to lose.'
Adam's opener was cancelled out by Cacau on the stroke of half-time, before Stuttgart surged into the lead after the break through Pavel Pardo.
Ferguson then drew level before Marica's late winner.
Adam added: 'I scored with my first touch - but I would rather have had the result.
'There are 'positives' to take out of the game. We suffered a couple of injuries and we came back from being 2-1 down, just as we'd come back at Ibrox. That shows the spirit we've got.'