Moody's (MCO) Moody's Ratings said Monday it placed Janus Henderson Group's (JHG) Baa2 long-term issuer rating and Janus Henderson US' Baa2 backed senior unsecured debt ratings on a review for downgrade status following the $7.4 billion acquisition offer of Trian Fund Management and General Catalyst.

Previous outlooks on Janus Henderson were positive, according to the ratings agency.

The agency said the proposed acquisition is expected to be financed with equity and debt, which may be "credit negative" if leverage rises.

Additionally, the ratings agency said concentrated private ownership is normally riskier than public ownership.