Millen saw his side gain a valuable point against Crystal Palace on Saturday but has a host of problems ahead of the game against a rampant Reds side.
"The players need some help," he said, quoted in the Bristol Evening Post. "We have nine lads injured at the moment and that is leaving us short on the bench.
"Jon Stead was on the bench at Palace but was not fit enough to play, and that left only three senior players among the substitutes.
"I need to bring in one or two new faces just to support the hard work the senior lads are doing.
"We have to be active, especially now that so many players are out injured. I want competition for places and, at the moment, we don't have that."