The GLG Japan CoreAlpha Fund was launched in November 1999 and has reached £1.1bn ($1.7bn) in size.
In February 2010 the GLG Japan CoreAlpha Equity Fund was unveiled as a currency-hedged replica of the then £698m CoreAlpha Fund, and has since reached $1.1bn in assets under management (AUM).
GLG said both funds would be closed to new investors from the end of March, subject to Financial Services Authority and board approval, but will remain open to redemptions in the normal fashion.
Richard Phillips, the head of UK retail at Man Group (which owns GLG), said: "The large cap high conviction approach of this strategy necessitates owning a relatively concentrated portfolio of stocks. Since the earthquake in Japan last March there has been a reduction in liquidity in the Japanese equity market.
"While this has not impinged on the team’s ability to manage portfolios with the desired degree of liquidity and flexibility, it has created a risk that performance could become constrained if inflows into the strategy increase."
The cap on the funds is set to be temporary and GLG plans to reopen them as soon as it is confident the market conditions in Japan will allow for normal trading, even in the event of a significant increase in AUM.
Both funds are managed by Stephen Harker and Neil Edwards, with the original fund UK-domiciled and the mirror fund Dublin-domiciled.