RBS and its partners Santander and Fortis plan to counterbid for LaSalle under a "go shop" sale period that runs until Sunday, the sources said. The offer will be conditional on them also buying the rest of ABN.
The court said that ABN Amro was not allowed to sell any of its subsidiaries without consulting shareholders first.
Dutch shareholders association VEB viewed the sale of LaSalle as "unlawful" because it said ABN Amro was "deliberately seeking to frustrate the possibilities of a better (takeover) bid
by other banks than Barclays."
The court ruling appears to give the advantage to RBS over Barclays.
"While this (ruling) isn't surprising, it is very positive for the European capital markets," said Magnus Mathewson, an analyst at Hitchens Harrison. "The (RBS) bid could well happen as early as today," he said, adding that Barclays had little hope of raising their deal.
"Barclays are on the sidelines now," he said. "Their offer has been trumped in a massive way."
He added that Bank of America might make a bid itself for ABN-Amro.
"BoA might be tempted to make a bid for ABN itself," he said. "They obviously really want LaSalle."