Clarke, in his letter to employees said, Navistar's board of directors is reviewing the proposal, he said.
"While we don't have any further detail to share at this time, we will make every effort to keep you informed as information becomes public," Clarke said in the letter.
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According to the national media reports, there is no assurance the deal will happen.
Bloomberg reports that billionaire investor Carl Icahn is the biggest holder of Navistar shares of the Lisle, Illinois-based company that builds International-brand trucks, school buses, defense vehicles and engines.
VW, based in Wolfsburg, Germany, owns an almost 17% stake in Navistar.