One of the three people arrested yesterday as part of a Financial Services Authority (FSA) probe into insider dealing has been reported to be an analyst at GLG.
The three arrests are not tied to any other insider-trading investigations that the FSA has already disclosed.
The employee has been suspended, Man said.
The news of the arrest comes as Man reported a drop in funds under management in 2012, falling to $57 billion (£37.1 billion) compared to $58.4 billion in 2011.
On the same day, Man Group, which took over GLG in May 2010 in a $1.6 billion deal, also told its shareholders 2012 had been a 'tough' year, issuing its final results on the morning news of the arrest emerged.
The group's funds under management pulled back slightly from $58.4 billion to $57 billion, as at the end of December, while adjusted profit before tax came in at $278 million.
Manny Roman, Man's chief executive officer, admitted: '2012 was another tough year for Man.'
He explained: 'Trading conditions were highly challenging as markets continued to be dominated by political uncertainties in Europe and the US and macroeconomic risks.
'Investor appetite remained muted and as expected there was a further decline in Man's product margin mix and revenues.'