The Reds missed out on a place in the UEFA Champions League when beaten by Tottenham Hotspur in last season's Europa League final and, after exiting the Carabao Cup at Grimsby Town, there have not been opportunities to hand more minutes to players.
Hence, the boss has reiterated it is an absolute priority to qualify for European competition next term, as United chase a fourth successive win, in Saturday's trip to Nottingham Forest.
One thing that has pleased Ruben, though, is the way those not in the starting XI are supporting their colleagues, even if he understands their desire for more playing time.