Nokia called the report "100 percent baseless."
Nokia shares have been in steep decline in the past two days after its latest failure to deliver on recovery targets.
Dealers said Microsoft shares also fell on the report, which appeared on the web site www.bgr.com, citing a person called Eldar Murtazin, whom it described as an industry insider.
Microsoft and Nokia struck a deal earlier this year under which the Finnish company will move to using Microsoft software in its phones instead of its own Symbian software. Nokia's new CEO Stephen Elop is a former Microsoft executive.
"These rumours are 100 percent baseless," Nokia spokesman Doug Dawson told Reuters.
The shares were 0.8 percent lower at 4.714 euros, having dropped as much as 10.2 percent earlier in an extension of Tuesday's 18-percent slump. Volume in the stock reached six times the 90-day daily average.