Forest defender Luke Chambers fired the only goal of the game at the City Ground just two minutes into the second half to condemn City to yet another defeat.
"We didn't have enough quality about our play in the final third of the pitch to trouble Forest as we might," Millen said.
"I thought that we had enough chances to get at them, even in the first half when we had a lot of opportunities on the counter attack.
"In the second half we had more control of the ball but more often than not our final ball or decision-making let us down.
"It was poor and that's the way it has been for the last few matches."
Source: PA
Source: PA