McDonald, a City fan who used to stand on the Kippax terraces, almost won control of Maine Road four years ago.
"I have been approached in the last few days by people who believe they have enough shares to carry the situation and are asking me whether I'm still interested in fronting the bid," McDonald said yesterday.
"But at the moment I'm committed to Sheffield United and want to see the job through, and that's getting them into the Premiership."
McDonald almost took over City at a Christmas Eve board meeting nearly four years ago, which saw him just lose out when the late Peter Swales was willing to sell out. After Francis Lee took control, McDonald moved to Sheffield United.
The approach to McDonald comes with City's major shareholder, Stephen Boler, reported to be willing to sell his interest in the club. If brewers Bass take control of Greenalls - as is being suggested - then Greenalls' shareholding at City would also come on the market, which makes City vulnerable to a takeover, as Lee and his supporters on the board do not have enough shares to block the move.
McDonald also said that when City drew 1-1 at Bramall Lane a week ago, he and Lee had discussions about the future at Maine Road.
"I had a little talk with Franny a couple of weeks ago and he is obviously down in the mouth about it all, and I understand Stephen Boler is now wanting to develop his life in South Africa and may want out.
"The situation from where I'm looking from is that the club was worth around pounds 12m when I was first involved. Now it's about three times that. I would have been able to buy the club then for about pounds 6m. The club is in no better position, in fact it's worse because it was in the Premiership, so from a club in a worse position it's now costing three times as much.
"But all this is hypothetical. I am a chairman of a public company [Sheffield United plc], committed to this club's success and getting promotion, and until that alters I am not in a position to even think about this.
"A lot of water has gone under the bridge since I was trying to buy into City. I am deeply committed to trying to achieve Premiership status for Sheffield United. But it is common knowledge that I'm a Manchester man and a City fan, and it has been sad to see what has gone on.
"I nearly won the day last time, and the people who have come in have not done what needed to be done. It needed looking at seriously."
Lee yesterday dismissed the possibility of another power struggle at Maine Road. "I had dinner with Stephen Boler recently but none of these points were raised. The stories are utter rubbish," he said.Reuse content