The Australian told the Glasgow Is Green Podcast that he was already doubting his place in the side under the former Hoops captain when he overhead a private chat between Mowbray and fellow striker Marc-Antoine Fortuné, which let him know in no uncertain terms that the boss preferred other attackers at the club.
McDonald would complete a £3.5million move to Middlesbrough a short-time later, where he once again teamed up with Gordon Strachan, the man who originally brought him to Celtic in the summer of 2007.
Mowbray, meanwhile, would leave Celtic before finishing his first full season. He was sacked by the board following a 4-0 defeat at the hands of St Mirren, with the club already well behind Rangers in the title race.
McDonald said of his dealings with Mowbray: “Everything was fine until he brought me into his office and asked me a couple of questions, just about me. I was thinking why are you are asking me? Why haven’t you done your homework? Why are you making me, uncomfortably, talk about my strengths and weaknesses?
“In the end, the conversation went like, ‘well, I don’t think you do this and I don’t think you do that’, and I just walked out the door. It was quite negative and I was just left wondering, ‘what on earth was that about?’ I don’t mind being told my negatives because you need to improve as a player, but there are ways and means of going about it. I just felt from then that I wasn’t going to be an integral part of his team.
“Every time he played me I scored, so he had a problem. He wanted to change it, but he couldn’t. And every time he did it wouldn’t work and I would come on and change it. He had a massive dilemma.
“There was a conversation that happened at a team talk. He was the first manager I had that would do video analysis. We would focus on the other side’s set-pieces before heading to the ground for the game, So we all finished that and were ready to leave, and I went to the toilet as everyone got on the team bus. Now, there was a fire exit leading down, and I was at the top of the stairs and Tony was down at the bottom of the stairs talking to Marc-Antoine Fortuné.
“There’s two ends to every stick, and looking back now I can see what he was doing, but at the time there was only one thing on my mind. He [Tony] was basically saying, ‘once he stops what he’s doing, you’re in the team. I fancy you more as a player, but we need to wait because I can’t just bin him.’
“He didn’t know I was there, but I let it be known I was there at the end. I didn’t say anything but I just walked down, and it was quite an awkward moment for everyone. From that moment on I just knew we weren’t going to get on. He’s the manager, so he’s not undermining me. But, at the same time, you’re not his player. So that stuck with me throughout that whole period.”
When McDonald found out about interest from Middlesbrough, who were also looking to sign Barry Robson and Gary Caldwell, his prior relationship with Strachan was a big factor in his decision to quit Scottish football for the English second tier.
Though it was an easy decision at the time, McDonald now regrets the move, wishing he’d stuck around at Celtic Park.
He added: “I had a manager who believed in me, which wasn’t what it felt like in the final six months at Celtic. I had a manager who’d brought me all the success I’d had until that point, who brought the best out of me, and I had someone who I believed in to be successful at Middlesbrough and to get the club promoted. So for all of those reasons, and the financial aspect, it was a no-brainer.
“Looking back I probably moved too early. I would have liked a little bit longer at Celtic.”
• Listen to the full episode of the Glasgow Is Green podcast here.