The LSE is unlikely to meet its targets for predicted volume growth, and even if it did, pressure on fees would hurt revenues, Nasdaq said.
In response, the LSE management accused Nasdaq of "self-serving criticism". It pointed out that the LSE offer was cheap, compared with the price-earnings ratios of its rivals Deutsche Börse and Euronext.
Nasdaq hit back later the same day, accusing LSE management of having "no real interest in taking part in a dialogue".
The deadline for shareholders to accept the Nasdaq bid falls on Friday. Nasdaq already owns 28.5% of the LSE.