MacDonald has been put in interim charge of Villa, after Sherwood parted ways with the Midlands club on Monday.
The Scot named the line-up and created the tactics for Villa’s League Cup tie against Southampton, which they lost 2-1 in midweek, and he admits that he was keen to make some alterations to Sherwood’s strategy.
“The game plan we had on Wednesday was slightly different to Tim’s but we knew this was the way we had to try and do things," he said.
“It didn’t work and that was my fault because basically they were my tactics which we got wrong.
“I make the decisions.”
MacDonald’s tweaks did not have the desired impact, as Villa crashed to a defeat against Southampton.
The Claret and Blues were rarely in the match, and their goal came too late to give them any hope of progressing.
It means that Villa have now lost their last five matches in all competitions, and the squad look desperately low on confidence.
Whether MacDonald will have any more time to implement his changes remains to be seen, as Villa will be hoping to have a new manager in place by the time they face Tottenham Hotspur on Monday evening.