Lieutenant General Azubuike Ihejirika is suing Dr Stephen Davis for alleging that the general supported Boko Haram extremists he was meant to be fighting in Nigeria.
However Dr Davis argues that his allegations have been well documented: "Iherijika was chief of army staff... from 2010 to 2014.
"You might like to look at the growth of Boko Haram during that time," he said in The Times.
Stephen Davis had travelled to Nigeria in 2014 following the kidnap of more than 200 school girls in Chibok.
Four months after their abduction Dr Davis accused a number of prominent Nigerians - including Lieutenant General Azubuike Ihejirika - of sponsoring terror.
General Iherjirika said these claims are false and has demanded an apology and damages.
His lawyers described him as a "gentleman," a "statesman" and a "world figure."
General Iherjirika is also suing the website that published the allegations and its editor-in-chief.
Dr Davis said that this suit comes at a time as the government in Nigeria is undergoing a purge and investigation into corruption in the military.
