"Michael has always been great like that," Ferguson said. "He is always phoning me and seeing how I am, and I phone him too asking for advice.

"He was always saying, 'Stick with it, see how the start of the season goes.'"

Ferguson was never keen on the idea of leaving Millwall, having enjoyed some great times with the Lions.

"I had the conversation with the manager in the summer and the door was left open for me to choose what I wanted to do really, but at that stage I'd had a lot of great moments with Millwall, getting promoted, and it's hard to walk away from that.

"I said to myself I want to give it another six months to January and we'll see how it goes from there. I didn't want to leave with any regrets and it's worked out quite well."

Ferguson was limited to cup matches and late substitute appearances at the start of the season, but since starting against Nottingham Forest on October 3, he has been a regular on Harris' team-sheets.

"It was a tough time not playing at the start of the season, and last season for the last couple of months," he said. "It's good playing regular football and gives you that bit of confidence."

Ferguson is now hoping to take that confidence into a big week for Northern Ireland.

O'Neill's side face the Republic in a high-profile friendly in Dublin on Thursday before Sunday's Nations League finale against Austria in Belfast, where they may yet still have a chance to avoid relegation depending on Thursday's results.

For now all eyes will be on the Aviva Stadium.

"I'm really looking forward to it," Ferguson said. "There's going to be a great atmosphere. It's just a game we're looking forward to and hope we can get to win.

"It's about being hard to beat. We're obviously playing away from home as well so can't just go all out attacking.

"We just need to be smart in the way we play. We've got great players here and we've shown in the past how good we can play together and we need to keep doing that."

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