Microsoft is worried that any sale of Nortel's patents could endanger the worldwide agreements it had with the company.
Google is offering $900m for the remnants of the company, and its 6,000 patents, and Microsoft is calling for any existing patent agreements to be transferred.
Microsoft warned that any sale would disrupt the development and enhancement of "various existing technologies", Bloomberg reports.
It holds worldwide licences for several Nortel patents.
Ink giant HP is also objecting to the sale on similar grounds: the need to protect existing agreements.
Nokia has also filed similar objections with the court in Delaware. ®