Cowley, who manages the £561m Old Mutual Global Strategic Bond fund, leaves in June and will be replaced on the portfolio by Christine Johnson and John Peta.
OMGI chief executive Julian Ide says: “I am grateful to Stewart for the guidance and stewardship he has given to Old Mutual over the last six years and for the commitment he invested in building our powerful fixed income capability.
“He has made a vital contribution to our management teams over many years, and particularly since I joined the company.”
But Morningstar says it no longer has “the conviction that [the fund] will outperform its peers on a risk-adjusted basis over a full market cycle”.
Morningstar highlights the fund’s unconstrained approach and Cowley’s imminent departure from the asset manager as reasons for the downgrade. It says: “This approach has produced very large performance deviations in recent years, such as massive underperformance in 2014, and a high risk profile, which makes the fund difficult to use for investors looking for global fixed income exposure.”
Last year, the Old Mutual fund lost 2 per cent versus a Global Bond sector average return of 5 per cent over the period.