Aberdeen edged into the second qualifying round of the Europa League despite a 1-0 defeat to Fola Esch in what was one of the club's worst performances and results in European competition.
Aberdeen survived a scare after Fola reduced the Dons' aggregate lead to 3-2 in the final minute of the first half, when Samir Hadji raced clear to finish emphatically.
Fola hit the inside of the post with 15 minutes left as Aberdeen were effectively left with 10 men when Willo Flood suffered a back injury with three substitutes on.
The Irish midfielder limped on and Aberdeen's passage was equally unconvincing, although Adam Rooney should have had a penalty late on and instead was booked for diving.
McInnes, whose side face Latvian side Ventspils in the next round, told RedWeb: "Fola potentially deserved more from tonight, I think they were excellent.
"Everywhere we were last week in terms of composed, determined, confident and energetic was lacking from the performance. I need to find out why that was, I take responsibility for that.
"We didn't look as if we were ready and we will need to look at our preparation both mentally and physically. In play we didn't look great, but we got through and I need to keep forcing that message home.
"It was extremely hot out there with the early kick-off, but we didn't have our normal energy levels. It was a collective, sometimes mentally that can play with you, but it was collectively a below-par performance.
"The players know that and are honest enough to admit that. I feel that we owe the supporters for that performance as we are better than that, but we've progressed to the next round and we aim to get better as we go along, but we are certainly better than what we showed."