Red Bull said Dan Fallows has been appointed head of aerodynamics, replacing McLaren-bound Peter Prodromou who is now on ‘gardening leave’.
The statement drew a swift response from McLaren, who announced at their car launch in January that Fallows had joined along with Prodromou.
“Dan Fallows has a legally binding contract with McLaren, and the matter is now in the hands of our lawyers,” said a spokesman for the Woking team.
Red Bull said Fallows had left them last year after working as aerodynamics team leader but had returned and was starting his new job with immediate effect.
McLaren announced last October that Prodromou would be joining them but Red Bull, constructors’ champions for the past four years, were determined to hold the much sought-after Briton to his contract.
They did not say when his leave would formally end.
Prodromou was McLaren’s head of aerodynamics until 2006, having joined that team in 1991, when he followed Adrian Newey to Red Bull.
McLaren have changed their leadership since Fallows agreed to join, with Ron Dennis retaking overall control and Eric Boullier appointed racing director in place of departed principal Martin Whitmarsh.
The team started the season with a second and third place in Australia for Danish rookie Kevin Magnussen and Jenson Button, pending an appeal by Red Bull who had Australian Daniel Ricciardo disqualified.
Red Bull have won the last four constructors’ and drivers’ championships, with Sebastian Vettel triumphant in the last nine races of 2013, but have started the season chasing dominant Mercedes.
McLaren failed to finish on the podium last year.
(Reporting by Alan Baldwin; Editing by John O’Brien and Ken Ferris)