Millwall's Under 23s were defeated 1-0 by Barnsley in the Professional Development League on Tuesday afternoon.
Aiden Marsh found the net in the 56th minute to hand The Tykes all three points at the Barnsley Training Complex.
Next up for Millwall's Under 23s is a home game with Sheffield United next Tuesday afternoon.
Millwall: Wright, Moss, Strachan, Duncan, Ransom, Penney, Davis, Walker, Alexander, Bate, O'Brien (Leahy 75'). Subs not used: Miller, Gillmore, Adom-Malaki.
