Man Group has hired a co-head of foreign exchange for its $21 billion flagship fund AHL, as the London-based hedge fund manager tries to revive performance at its key computer-driven unit.

Ravi Chari, who has worked for 12 years in systematic trading at hedge funds, joins Man from computer trading firm IKOS, where he headed its futures and foreign exchange funds, Man said in a statement on Thursday.

Chari will work in the newly-created role alongside David Denison, the current head of foreign exchange at AHL, which employs around 130 people.

It's an area where we see a lot of opportunities, said a Man spokeswoman, adding that around one-fifth of AHL's portfolio is in currency trading.

The hire comes after a difficult period for AHL, which -- despite Man's $1.6 billion purchase of fund firm GLG in 2010 -- is still key to its success. Last year around 70 percent of Man's revenues were generated by AHL funds or funds that allocate to AHL.

The fund tries to make money following trends in global futures markets but last year it fell 6.4 percent as its programmes focusing on short-term market movements were hit by market volatility. So far this year it has lost 2.1 percent.

Man Group's shares have also suffered, partly as a result of AHL losses, and have roughly halved since September. At 1136 GMT they were 1.9 percent lower at 113.6 pence.

(Reporting by Laurence Fletcher; Editing by Jon Loades-Carter)