"Anybody who has gone through that incredible transformation is going to be feeling the most unbelievable pressure," he said during a radio interview this week.
Piers said he had been told the 48-year-old church worker had been "in tears repeatedly" over negative stories which appeared in the press. He told ITV's News At Ten: "On Wednesday she was actually going to leave the show, packed her bags to go, because she couldn't see the point in going on if all she was going to get was all this sniping."
"I think there's a lot of cynicism now building up about Susan, a lot of unnecessary criticism about her and we should give her a break. She's two days away from the biggest show of her life, the biggest moment of her life."
Susan's brother John said his sister is having a tough time, partly due to the lack of support she has received. "Susan is finding it very difficult at the moment. She has become a global sensation and is finding that she doesn't have any of the protection and support that big stars normally do."
"She is just a normal woman from a small village in Scotland, who all of a sudden is being forced to cope with this on her own."
The middle-aged star, who has admitted to having a crush on judge Piers, has reportedly been given a secret bolthole to escape public scrutiny ahead of the Saturday final of the TV star search. ITV bosses are also considering shelving her appearance if she is deemed too unwell to perform, according to newspaper reports.