While GTA IV grossed over $500 million in opening week sales and has been cited by Take-Two as an example of why EA’s $2 billion offer to acquire the New York-based publisher undervalues the company, a new report speculates that a slowdown in the game’s sales could provide EA with greater leverage in its takeover pursuit.

Last month industry sales monitors the NPD Group, GfK Chart-Track and Enterbrain released a multi-continent report that pegged GTA IV as 2008’s bestseller to date with 6.3 million units sold, a figure now thought to have swelled to 8.5 million units, despite the fact that the game only released in late April in the US and UK and has yet to hit the Japanese market.

However, the latest title in Take-Two’s flagship franchise, which is central to EA’s bid to acquire the company, was only the 46th bestselling game in the US during August according to new NPD rankings, a factor that could improve EA’s chances of securing a takeover, CNN speculates.

Despite the slowdown, Take-Two CEO Ben Feder said during the company’s third-quarter earnings call last week that he was confident GTA IV sales would pick up coming into the holiday season.

“Rockstar is launching a new marketing and PR campaign which will start in the fall and extend into the holiday season,” he said. “Also as a must-have game for all fans of interactive entertainment, GTA IV we believe should receive a boost from the ramp up in hardware sales during the upcoming holiday season.”

EA and Take-Two recently signed a confidentiality agreement that barred either party from publicly disclosing the status of any negotiations relating to their ongoing acquisition talks. The pair are locked in discussions as they look to reach an agreement on a deal that best suits both parties, with Take-Two having previously labeled EA’s long-standing offer for the company of $25.74 per-share “inadequate in multiple respects”, and EA refusing to budge, eventually letting the bid expire after a number of extensions.

A potential EA takeover of Take-Two was greenlit by the Federal Trade Commission in late August.