The host, who was replaced at the last minute by This Morning's Ruth Langsford, is said to have collapsed backstage while "crying uncontrollably", just days after revealing she was divorcing second husband Steve Toms.
"Andrea has had a bit of a week of it and it all caught up with her today. She had a panic attack half an hour before the programme started and couldn't stop crying," a source told The Mirror.
"It was clear she wouldn't be able to take part and so she went home. It's been a horrible time for her but she'll be fine. We fully expect her to be back on the programme next week."
Speaking of her split earlier this week, McLean said: "I'm still in shock. When I hear myself talking about 'my first marriage breakdown' then 'this time round', the words are like a stab in the heart. Because I simply can't believe I'm in this position again."
McLean has apparently suffered from panic attacks since a crazed fan pushed her down an escalator ten years ago.