LJUBLJANA (Reuters) - Pop star Madonna has canceled her concert in Ljubljana, Slovenia scheduled for August 20, the tour manager said on Friday.

Local media cited poor ticket sales as the main factor, although promoters denied this was the reason.

It is the second concert Madonna has canceled since July. A performance in the southern French town of Marseille was scrapped after the stage being built for it collapsed, killing two workers.

"The reason for the cancellation is unforeseen logistical difficulties," said Laszlo Borsos, managing director of Live Nation in Budapest, overseeing Madonna's tour in eastern Europe.

"There is no problem with ticket sales, absolutely."

Slovenian media reported the concert had to be canceled as promoters had sold only 7,000 of a planned 63,000 tickets in a city with a population of 250,000.

In 1997 Michael Jackson was set to play the same location, but his concert was axed amid poor sales.

According to Madonna's website www.madonna.com, of 12 remaining concerts on her Europe tour which ends in Israel, only Sunday's upcoming concert in Gothenburg, Sweden, is sold out.

In cities such as Belgrade, where Madonna has never performed before, organizers are advertising heavily in the lead up to a concert later this month.

(Reporting by Manca Ulcar in Ljubljana and Adam Tanner; Writing by Ivana Sekularac; Editing by Michael Roddy)