Louis van Gaal will not "voluntarily step aside" for Jose Mourinho.
The under fire Manchester United manager is coming under increasing pressure at Old Trafford after seeing his side's Premier League title challenge crumble in the space of a month.
Mourinho has been heavily tipped to succeed him if the 64-year-old is shown the door, with claims that the former Chelsea manager is convinced the job is his.
Van Gaal was a mentor to the 'Special One' when making him his assistant at Barcelona in the 90s.
The the two men retain a huge respect for each other, but Van Gaal's biographer, Maarten Meijer insists the Dutchman is determined to fight on.
"The British media have suggested one alternative after another as replacement," he said. "Carlo Ancelotti and Pep Guardiola are just some of the names that have been mentioned.
"The most surprising suggestion has been Jose Mourinho.
"This is the man who was fired mid-season, after taking Chelsea to the threshold of the relegation zone.
"Van Gaal and Mourinho are friends, but he is not going to step aside voluntarily for his Portuguese colleague, or for anyone else."
Van Gaal reportedly offered his resignation in December - but that was rejected United's hierarchy.
Now he is intent of repaying the faith shown in him by executive vice chairman Ed Woodward.
And Meijer, who studied his countryman closely for his book, 'Louis van Gaal: the Biography,' insists the former Ajax, Barca and Bayern Munich manager can handle the growing criticism of his troubled reign.
"In some ways, his experience is at Manchester United is nothing new," he said. "At Barcelona and at Bayern he was variously criticized as a dogmatist, out of step with the club culture, or a lunatic, out of touch with his players.
"Given time, he proves his mettle and pulls his teams through the doldrums to title wins.
"His time at AZ-Alkmaar was maybe the most striking illustration of the transformation a Van Gaal-coached team can go through.
"At the end of the 2007-08 season, the team was languishing in 11th place and Van Gaal had to be convinced by his players not to walk out on the job.
"In the 2008-2009 season, AZ won the title, 11 points clear - breaking the nearly three-decade title monopoly of Ajax, Feyenoord, and PSV."
Meijer added: "Some suggest Van Gaal is not equal to the task and is overwhelmed by the pressures he encounters at Manchester United.
"Is the pressure at Old Trafford that much greater than at Camp Nou or at the Allianz Arena? Hardly."