With Bo’ness winning the game 4-2 after 58 minutes, Miller – who had scored twice – sustained the agonising injury following a challenge by Wick defender Danny Mackay.
Describing Mackay’s foul on Miller, BU boss Christie told the Falkirk Herald: “The ball goes wide, Zander goes to beat the guy and he just takes him down. The ref sprints over and immediately shows a yellow card which he then doesn’t change to a red when he sees the severity of it, which he should do.
"So that was a terrible decision. Zander has broken his ankle and he’s getting it double plated, he’s getting screws in.
"It was a distressing scene for Zander. His family were there and I think everybody at the game was just worried about Zander’s welfare and how he was. Thankfully he’s going to be fine.
"My physio Luisa (Robertson) is telling he he’ll be in a cast for six to eight weeks. A special mention for her as she calmed things down, noticed straight away that it was too serious to move Zander so we had to put him in a splint and wait for an ambulance. She was very professional and made a bad situation better.
"He’s paying for that 45-minute wait. It would have been unimaginable, his pain.
"It was not a good day for the club. Zander’s a big player for us. I think he’s the top scorer in the league in all competitions or very near it.
"So he’s a big, big loss for us and such a wonderful guy and popular player about the place so we’re all very concerned for him.”
Without Miller – who faces a long rehabilitation period before he can return to training – the BUs then won 4-1 in Tuesday night’s rematch at Newtown Park, booking a second round clash at Edinburgh City on Saturday, October 23.
Bo’ness goals came via Kyle Wilson’s 11th minute shot from a tight angle, Kieran Anderson’s fine solo goal on 46 minutes, Nicky Locke’s fine finish three minutes later and – after Wick had had a man sent off but pulled it back to 3-1 with a penalty – a late Ryan Stevenson spot kick after a Wick player had handled the ball.
Christie said: “We played very well again. There were a lot of good performances.
"Kyle Wilson played very well, Mikey Gemmell was outstanding, there wasn’t a failure.
“Kieran Anderson had a good game, playing with an injury for a while because we were down to the bare bones.
"So it was a good result and I don’t think anybody could dispute we were the better side.
"Wick only travelled down with 11 players – their manager (Gary Manson) played – we had 12.
"There’s no doubt it was a challenge for Wick to get a team on the park.”
Bo’ness resume their Lowland League campaign at home to Civil Service Strollers on Friday, KO 7.45pm.
"Strollers are going very well and play in a specific way,” Christie said.
"We need to be at the usual, we need to be at our very best if we’re going to get anything from the game.
“Miller is a big loss but the other strikers played well on Tuesday night and there’s an opportunity for them to go and claim a place because of what happened.”