Borse Dubai, which holds a 20.6 percent stake in the LSE and is owned by the ruler of the Gulf Arab emirate, will become the single largest shareholder in the new entity with an 11.3 percent stake if the deal is completed.

The proposed deal between the two exchanges has run into foreign ownership concerns in Canada.

"Borse Dubai hasn't been asked by any party to trim its stake in LSE," the source said, speaking on condition of anonymity.

The Qatar Investment Authority (QIA) owns a 15 percent stake in LSE and the two combined would end up with a roughly 20 percent position in the new combined company.

Ontario's finance minister last week voiced concern about the ownership issue, saying the exchange was a strategic asset.

"We do business with the Middle East," Dwight Duncan was quoted as saying. "I am just not sure I want them owning our stock exchange.

On Tuesday, a UAE newspaper said Borse Dubai would consider selling down its stake in order to reduce its ownership in the joint exchange to less than 10 percent, citing a senior Borse Dubai official. The newspaper did not name the official.

Borse Dubai's Chairman Essa Kazim declined to comment on the report when contacted by Reuters.

The UAE newspaper report said Borse Dubai executives were also not completely confident that the deal between the LSE and TMX will produce long term value. One executive said Borse Dubai would only sell if it could find a strategic buyer at the right price.

"We're not going to sell down just to make it easier for Xavier Rolet (the LSE chief executive) to do the deal," the exchange executive told The National newspaper.