Not nutrient deficiency, no, its not been in long enough to even root into the soil, unless the deficiency is in the soil the plant was sold to you in. Much more likely to be too dry at the roots, these plants don't cope with drying out, but dig it up, gently, to check whether the rootball is dry - if so, increase your watering. Check for rot at the crown, which may have been present when you bought the plant, just not showing symptoms.

I would also say lack of watering. They are marginal pond plants and like constant water, but dry in winter.