The former Celtic scout has blasted the club's recruitment policy.
The Hoops have undertaken a policy of buying low and selling high in recent years as they have looked to make maximum profits from their players.
It has worked on several occasions, with the likes of Victor Wanyama, Fraser Forster and Virgil van Dijk all making big moves to the Premier League.
As a result though, the general quality of the squad has decreased, with the club going from qualifying for the Champions League knockout stages under Neil Lennon to failing to get into the competition at all.
That has disappointed the fan base, and former scout McGuinness, who says the likes of Carlton Cole, Nadir Cifti and Colin Kazim-Richards are not good enough.
“The overall talent pool within the squad has dropped because of it. This in turn has made the supporters start to ask questions.”
“The pressure is on to make sure that the players being identified and monitored are of the level that Celtic should aspire to.”
With a new manager incoming this summer, it will be interesting to see if Celtic continue their current recruitment policy.
More importantly though will be the return of Rangers to the Scottish Premiership, with many expecting Mark Warburton’s side to challenge for the title.
That would be the first competition the Hoops have had since Gers demotion, and the Hoops would have to spend to ensure their recent dominance.