The 19-year-old got the chance from the start and played 61 minutes before he was replaced at the position 2-1 to United.
In the 78th minute, Brentford equalized and the match ended 2-2.
Also in Saturday's training match against Queens Park Rangers, Elanga became the goal scorer when United fell 2-4.
Anthony Elanga, son of former MFF player Joseph Elanga, made his Premier League debut for United on 11 May against Leicester (1-2) and scored his first league goal against Wolverhampton (2-1) on 23 May.
CLIP: Elanga strikes in U21 debut (June 3)
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Anthony Elanga Photo: Bildbyrån