Paris - French rugby giants Racing 92 and Stade Francais, winners of the last two Top 14 titles, on Monday announced a shock merger that will leave many top stars looking for new teams.
Racing and Stade Francais are two of the biggest rivals in the French championship and the merger from next season came as a lightning bolt for European rugby.
Racing's real estate billionaire owner Jacky Lorenzetti said tough "choices" would have to be made about which players to keep.
Lorenzetti has spent heavily on top talent such as All Black legend Dan Carter, now in the second and final year of his deal. Racing won the championship last year, but are now slumbering in seventh and Carter was jeered off the pitch after a weekend defeat to leaders La Rochelle.
Stade Francais counterpart Thomas Savare, a finance and credit card technology tycoon, has likewise paid heavily for the likes of Italian captain Sergio Parisse, Australian scrumhalf Will Genia and South African flyhalf Morne Steyn. His team, triumphant in 2015, are currently 12th.
Lorenzetti said in a letter to supporters that the two coaches Laurent Travers and Laurent Labit would have to "make choices".
"Merit will be the criteria, probably youth and the factor of being selectable" for France, Lorenzetti said.
He added that the two clubs would maintain their youth and amateur sides but "merge the professional teams."
Lorenzetti and Savare would serve alternate terms as head of the club. But the Racing chief said the aim was to have a single powerful club for the Paris region.
Opposition to the merger came quickly, notably among Stade Francais players with some calling for protest action. French international fullback Eric Bonneval tweeting: "13/03.2017: END."
"This is not a merger. Stade Francais has been bought by Racing... This is the death of our club... " said lock Paul Gabrillagues.
Lorenzetti said he wanted "to build day after day the reference of French rugby."
"This association, effective from next season, will give birth to a new club that preserves the roots of Racing 92 and Stade Francais Paris, while expanding the means for youth and French rugby," said a statement announcing the plan.
But the deal will have massive implications for the Top 14 and European club rugby.
Each has built, or is building, a new stadium as well as big squads. No immediate details were given of their ground plans, but Lorenzetti and Savare were to speak later Monday at a press conference.
Racing were slumbering in France's second division when Lorenzetti bought them in 2006. Savare took over Stade Francais in 2011 when they were threatened with bankruptcy and relegation.
The clubs have spent hundreds of millions of euros on redeveloping and acquiring new players since 2010.
Stade Francais's Jean Bouin stadium was redeveloped in 2013 and reopened with capacity increased from 13,000 to 20,000.
Racing are building a new €220 million 32,000-seat stadium in the La Defense business district. It should have opened in January but this has been put back to the end of the year.
The French National Rugby League (LNR) did not immediately react to the news, saying it was waiting to hear details from the two clubs. But the killing off of one Top 14 team means that the 13th placed XV -- currently Grenoble -- will now probably avoid relegation.
Racing and Stade Francais were among the first clubs created when rugby union was introduced to France in the 19th century. Racing won the first championship final against Stade in 1892. Stade got their revenge the following year.