While McDonnell was struck down by injury in the latter stages of the season Magnus impressed in Andy Graham’s side, scoring twice in ten League One appearances in Clackmannanshire.
Mackenzie will now move to the William Hill League Two new boys from Lanarkshire for the forthcoming season and he has already pulled on the Kilby kit as a trialist.
He was part of the team which defeated Neil Lennon’s Dunfermline in a friendly at the end of last month.
The loan deal will see Magnus train twice a week with East Kilbride and spend the rest of his week with the Spiders.