Contador is among an elite group to win all three major tours
Astana team leader Alberto Contador has admitted Lance Armstrong's arrival may force him to move to a rival outfit.
Armstrong came out of retirement to work with Johan Bruyneel, the man who coached him to his record seven Tour de France victories, at Astana.
But neither Armstrong nor Contador, who won the 2007 Tour, are likely to be happy for anything other than team leader status.
"If I am not happy I will change teams," said Contador.
When news of Armstrong's surprise return to the sport broke earlier this month, Contador said he would "welcome him with open arms".
But that stance seems to have changed after Armstrong officially signed with Astana.
"The team has said it has complete confidence in me, but this is a particular situation and I will have to see what happens in the coming weeks to then decide what is best for my future," said Contador.
"Four weeks from now the situation could be completely different.
"I spoke with Johan about the Tour next year and he said there is no problem and that I will be the leader, but Lance Armstrong is a champion and I think he will want to race to win.
"I am sure that he also wants to be the leader of the team."
The 25-year-old, who won the Tour of Spain and the Giro d'Italia this year, is contracted to Astana until 2010.
"I respect Armstrong. He has done incredible things, but I don't think that I have to prove to anybody that I should be the leader," said Contador.
"I want to be sure the team guarantees that I will be in the Tour as the team leader."
Armstrong has acknowledged Contador as "the best rider on the planet right now".
"We have to understand that and respect that," said Armstrong.
"I'm not sure I can ride that fast right now. I hope it works out."
One rider who believes there could be problems for the Astana team is the Republic of Ireland's 1987 Tour winner Stephen Roche.
"I could see (Contador) walking away. He's finally getting credibility and now next year everybody will be talking about Armstrong," Roche told BBC Radio 5 Live.