The youth fashion label is looking to raise its profile and distinguish itself from the main Diesel brand.
55DSL's head of marketing, Kristian Kristiansen, has approached agencies in London and France, but has yet to draw up a shortlist.
The Amsterdam agency KesselsKramer was the incumbent on the account.
In April, Diesel's main fashion brand ended its four-year relationship with Kessels-Kramer and handed its pan-European account to the Havas-owned ER27. It is now briefed to create a press campaign to launch Diesel's autumn/winter collection.
The Paris-based agency won a pitch against DDB London, This is a Thing (Red Cell Italy), Publicis and KesselsKramer.
55DSL launched in 1994 and is distributed globally. It has its strongest presence in the UK, Japan, Italy, Germany, the US and France.
The brand has four flagship stores in New York, London, Milan and Tokyo.
55DSL targets young, fashion-conscious people interested in action sports and urban culture.