Large losses within H2O Asset Management during recent market volatility have hurt the share price of Natixis, which owns a 50.1% stake in the London-based firm.
H2O's flagship Multibonds fund was down 20% on Monday alone, according to the Financial Times, bringing losses since its February peak to 40%.
Analysts said the French bank's share price slide reflected the importance of H2O in the eyes of investors.
A Barclays note said: "The shares have lost some €1.7bn of relative performance since Thursday which, given the €200m earnings contribution of H2O, doesn't seem particularly unfair if the market factors in longer term impairment of the franchise."
H2O made headlines in 2019 after it emerged the firm had put more than €1bn of investors' money into illiquid bonds linked to Lars Windhorst, a controversial German financier, triggering €8bn in outflows from its funds and prompting its founder Bruno Crastes to vow that he would never gate them.
Analysts at Barclays added that "clearly the risk is of further sizeable outflows in that context, particularly given the prior commitment of management not to gate".
Natixis shares closed down 4.8% on Wednesday (11 March), surpassing its index's losses of 0.6%, taking the French bank's share decline so far this year to 40%.