Activist hedge fund investor Carl Icahn is gearing up for a second board challenge at Ilumina as he looks to oust directors at the gene-sequencing company just months after shareholders elected one of his director candidates, according to a report by Reuters.

The report cites a letter sent to fellow shareholders by Icahn on Monday as revealing the plan less than 24 hours after Illumina said it intended to sell blood test manufacturer Grail.

Icahn is a longstanding critic of Illumina's $7bn acquisition of Grail which he blames for a 75% drop in Illumina's share price which he says has wiped out some $55bn in shareholder value.

The Grail takeover was central to his previous proxy fight which saw one of his portfolio managers, Andrew Teno, elected to Illumina's 11-strong board.