Manchester United head coach Ruben Amorim has said he and his staff knew before kick-off "that our team would struggle" against Brentford's physicality and set-piece prowess during their 4-3 defeat at the Gtech Community Stadium.
Brentford's victory on Sunday piled more misery on United' difficult campaign and condemned Amorim's side to a record 16th Premier League defeat this season.
Mason Mount had put the visitors in front in west London before they failed to clear a long throw-in from Michael Kayode. Mikkel Damsgaard made sure to capitalise and his shot deflected off Luke Shaw for an own goal.
Kevin Schade scored two more headers to put Brentford 3-1 up as United struggled to defend crosses into the box. The first of which irked United as it occurred when defender Matthijs de Ligt had gone down on the edge of the box clutching his leg after a challenge but referee Anthony Taylor did not stop play, allowing Brentford to score.
"The game is a little bit of a reflection of our season. We started quite well, controlling the game, not creating big chances, but controlling the pace of the game," Amorim told a post-match news conference.
"We suffered a lot through throw-ins and set pieces, but we already knew that our team would struggle against this team because we didn't have the height that would be necessary for this kind of game. They scored twice in these kind of moments, even with Mattha [De Ligt] on the floor [with an injury].
"In the second half, I felt that we were near the draw and then we suffered a goal and then like other times, we disconnect and then another goal five minutes later.
"We pushed forward and scored twice, but we didn't have the time to do better."
Amorim named a much-changed starting XI, with 17-year-old Chido Obi becoming the youngest player to start a Premier League match for the club.
With an average age of 22 years and 270 days, United's starting XI was the third-youngest any side has named in Premier League history. Amorim's team rank only behind Middlesbrough's team against Fulham in May 2006 (20 years and 181 days) and Arsenal's line-up for a clash with Portsmouth in May 2009 (22 years and 237 days).
Amorim's changes came four days before United's Europa League semifinal second leg meeting with Athletic Club on Thursday. United won 3-0 away in Spain in the first leg in midweek.
Asked if the two halftimes substitutions he made -- Leny Yoro and Amad Diallo replaced Patrick Dorgu and Shaw -- Amorim said: "With Mattha [De Ligt], we don't know what will happen on Thursday if we don't have Luke Shaw available, then we can have a problem as we won't have enough defenders for the game."
Information from Reuters and ESPN's Global Sports Research contributed to this report