The Celtic legend is adamant that Forster is an improvement on the long-serving Hoops man.
Forster arrived as a late transfer window signing on loan from Southampton, following an injury to previous club number one Scott Bain.
Despite a lack of football over the last couple of years, Neil Lennon has trusted him to immediately come into the team at the expense of Craig Gordon.
Gordon was a regular pick during Ronny Deila's and Brendan Rodgers' time at the club but was unceremoniously dropped in January.
Hay thinks that the addition of Forster adds serious quality to the Hoops squad.
As quoted by The Evening Times, he said: "He may not have had a lot to do at Ibrox, but his presence is something that will settle the Celtic backline down.
"I am a fan of Craig Gordon, but I think that Forster is currently at a different level and he will add quality between the sticks."
Will Forster keep his place?
It's certainly going to be interesting to see whether Lennon reverts to Bain when he recovers from injury or sticks with the Southampton man.
Forster has a long history of successful performances for Celtic and was a real favourite during Lennon's first spell at the club.
On top form he's an exceptional shot-stopper and as Hay notes, he has excellent presence in the box.
There's a reason he holds the Scottish top-flight record of 1,256 minutes without conceding a goal.
Whether he proves he's on 'a different level' to Gordon remains to be seen. It's important to remember he's barely been tested in his two appearances so far this season.
However, the initial signs suggest that the Celtic boss sees him as his number one.
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