Having both seen their loan moves confirmed last Tuesday, Cardines and Mustapha made an immediate impact by featuring for their new clubs just days later.
Cardines was introduced just before the hour mark on his Bristol City debut as the Robins – reduced to 10 men – trailed Millwall 2-0 in the Championship at Ashton Gate.
The 20-year-old received a warm welcome from the home supporters, but City were unable to find a way back into the game.
Cardines will hope for another opportunity when the Robins travel to Birmingham City on Saturday (KO: 12:30 BST).