The woman contacted former police superintendent Finn Abrahamsen with the tip-off on Monday, after the ex-policeman appeared on Norway's TV2 channel to discuss a new suspect in the long-running case.
"There was a lady who had been on holiday in Spain two and a half years ago," Abrahamsen told TV2. "At a mall, she believed she observed the girl with an older man, and was quite sure about this."
He said that the tip-off, coming two years after the alleged sighting, would be of little use to police.
"When it comes so long after the event, you could say that it's ok that you get to hear it. But on the other hand there's not much you can do with it."
The news comes as nearly 1,000 people have contacted London's Metropolitan Police with information about the new suspect in two new e-fit images released by investigators in an appeal on Monday.
"We have now had over 730 calls and 212 emails as a direct result of the specific lines of enquiry we issued yesterday concerning events in the lead up to, and on the night of Thursday 3rd May 2007 when Madeleine was abducted," Deputy Chief Inspector Andy Redwood said.
“Detectives are now trawling through and prioritizing that material. This will take time. We continue to appeal for information and I will be repeating similar appeals in Holland this evening on a programme called Opsporing Verzocht, and in Germany tomorrow night Aktenzeichen XY...ungelost."
"The MPS [Metropolitan Police] is offering a reward of up to £20,000 for information leading to the identification, arrest and prosecution of the person(s) responsible for the abduction of Madeleine McCann from Praia da Luz, Portugal on 3 May 2007."
He said people with tips should call 0800 0961011 in the UK, or +442071580126 from abroad, or send emails to Operation.Grange@met.police.uk.
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Madeleine McCann was just three years old when she went missing, meaning she would now be eight years old.
A new police reconstruction of the events is below.