Play off hero Alexander, who suffered a brain aneurysm in November 2003, went to hospital during the Silkmens game with struggling Bournemouth.
Macclesfields chairman Mike Rance told media: "It's purely precautionary. Keith wasn't feeling too well in midweek and he wasn't feeling that great before the game so we decided it was best to take the safest option."
Alexander took City to four consecutive play off finals before a move to Peterborough. His time there was curtailed after just six months, despite signing players like George Boyd, Craig Mackail Smith and Aaron Maclean.
He resurfaced at Bury as Director of Football but left when Chris Casper lost his job. However he found himself at lowly Macclesfield Town and has since set about reviving their fortunes.
Everyone at LCM wishes Keith the best, and hopes this is purely a precaution and that he is clear of his health worries.