(Adds background, details) A consortium led by Macquarie Group...

(Adds background, details)

A consortium led by Macquarie Group Ltd (MQG) has made an offer for Tatts Group Ltd (TTS), disrupting an agreed deal between the lottery operator and Australia's biggest bookmaker, Tabcorp Holdings Ltd (TAH), a source familiar with the situation said.

The offer from Macquarie and pension funds includes a mix of cash and shares in a spinoff company, the source told Reuters, adding the Tatts board had yet to decide if it offered superior value to a A$6.4 billion ($4.80 billion) cash-and-scrip bid from Tabcorp.

Tabcorp in October agreed to acquire lottery operator Tatts to create a gambling powerhouse in an effort to fend off a growing challenge from overseas online rivals.

In November, Tabcorp purchased control of around 10 percent of its takeover target Tatts for A$638 million, at which time a source familiar with the situation told Reuters that the share purchase by Tabcorp was meant to make it harder for an interloper to break up the agreed deal between the pair.

The Tabcorp offer, which remains subject to approval from Australia's competition regulator, will require the approval of 75 percent of Tatts shareholders. ($1 = 1.3340 Australian dollars)