The 33-year-old scored the opener in Wednesday's 2-1 Carabao Cup win over MK Dons.
"This man is on fire, that's how it is," said the Reds boss. "He helps a lot and he is a real model for the young players.
"If he could play every day, Millie would be like this every day, so that is brilliant.
"We could have done better in that final period but we started well as a team but then we got a bit stiff.
"We had to force the goal and then you saw Millie (score). The team lacked rhythm and experience and the player with the most rhythm and experience was the best player on the pitch. It was pretty obvious."