The Australian prop was sin-binned after the fight with James Greenwood in the 71st minute of Friday’s 32-16 win over Hull KR and the match review panel has now also handed him a Grade C repeated punching charge.
If the Super League leaders do not contest it, he will miss Thursday’s trip to Warrington Wolves as well as a home fixture with Salford Red Devils.
However, Powell said they are considering their options.
Friday's game finished in bizarre circumstances with Castleford down to 12 men and Hull KR reduced to just 10 with four players sin-binned in two separate incidents.
But Millington, 32, is the only player charged and, asked if they will challenge it, Powell said: "Potentially.
"I have to have a chat with (director of rugby) Jon Wells tonight before we make a decision.
"But I think there's potential there for that.
"It's obviously disappointing from our point of view as he's one of our top-line players so he will be a miss for us."
It was also out of character for the experienced player and Powell added: "There was a fair bit of niggle in the game, if I'm honest, from a couple of players.
"He's disappointed. We had a good chat about it; it's not something you see from us and our players. We're a pretty disciplined group.
"It's disappointing but it happens; it was a pretty edgy game and it boiled over a couple of times so there are some lessons there for us."
Powell says utility forward Alex Foster should be OK to return to action at Warrington after training today but England loose forward Adam Milner has not trained yet after the injury he suffered in their previous win against London Broncos.
"I'm hopeful but not certain on Adam," he added.
"He's a little better so we'll see tomorrow and on Wednesday and he'll have further treatment."
The only other player to face a charge from the match review panel is Hull FC front-row Mickey Paea.
He has been charged with a Grade A raising his knees in the tackle on Huddersfield Giants’ Aaron Murphy during Sunday’s 28-8 win.
However, he received a zero match penalty notice - so can face Leeds Rhinos on Friday - and was also cautioned for a similar offence on Kruise Leeming later in the same game.