Managing director David Walker said at Turin motor show that Lantra sales were likely to slip to around 3,000 in the UK this year.
He hoped the replacement for Lantra would raise UK sales to more than 5,000 units, relying strongly on fleet market interest.
The new model is expected to be named the Elantra across Europe - it is badged Avante in South Korea where it went on sale in April.
New Elantra, which has a Sonata-style front, is bigger than the Lantra, taking it into the Vectra/Mondeo marketplace. It will be launched in the UK as a 5dr only, though Hyundai UK is debating whether to take the 4dr.
No estate version is planned and Mr Walker believes that role will be filled next year by the Accent-based MPV. The Elantra will be launched internationally with 1.6 and 2.0-litre petrol engines and a 2.0-litre diesel.