Thomas Frank lamented Brentford's second-half performance as the Bees slipped to a 2-1 defeat to Manchester United at Old Trafford last weekend.
The West Londoners entered the break 1-0 up courtesy of Ethan Pinnock's contentious header at the end of the first-half, with the Jamaica international rising to meet Mikkel Damsgaard's corner while Red Devils defender Matthijs de Ligt was being treated for a head wound off the pitch.
But it would be United who would claim the spoils at the Theatre of Dreams with Alejandro Garnacho levelling the score two minutes after the restart and Rasmus Højlund's 62nd-minute effort - his first Premier League goal of the season - proving the winner.
And having witnessed his side surrender their lead and concede twice in the opening 20 minutes of the second half en route to defeat, Frank could not hide his disappointment.
He said to club media: "It was a good first half, I was very happy with that, I thought we were the better team in that period of the game against a good team,".
"We went 1-0 up, but it's so frustrating and annoying that they scored after two minutes of the second half - if they don't do that, you don't know what would have happened. But fair play to Manchester United.
"I thought that we were way too passive. But we are at Old Trafford, they have some top players.
"After the first goal, I felt like we lacked a bit more character. If we want to win here, we need more. Unfortunately, not enough of our players hit a high enough level in the second half."
Defeat in Manchester sees United rise above Brentford to sit 12th in the Premier League standings, with the Bees now one place below.
But one bright spot for the West London side was the return of Yoane Wissa.
The Congolese international suffered an ankle injury during Brentford's 2-1 defeat to Manchester City in September but made his return to the pitch against Manchester United last weekend, coming on as a substitute for Keane Lewis-Potter in the 65th minute.
The forward is Brentford's second-leading scorer in the league this campaign with three goals in five appearances, behind only Bryan Mbeumo, and Frank was delighted at Wissa's return from the sidelines.
He added: "Very happy to see him back on the pitch. We need our key players ready and we need enough to have something to shoot with from the bench."
Brentford next welcome Premier League newboys Ipswich Town to Gtech Community Stadium on Saturday.
The West Londoners have yet to taste defeat at home in a league game this campaign and will fancy their chances against the winless Tractor Boys.
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