"The team have given me assurances that I will be the leader, but I want to be doubly sure," he told Marca Sports Daily. "I want to see exactly how this is going to pan out. If I am not satisfied with the way it is going, then I will leave."
Seven-time Tour de France winner Armstrong announced his return to competition earlier this month and the Kazakh team has confirmed that he will hook up with them for several races.
Contador, who won the Tour de France in 2007, is the current team leader at Astana. He has given conflicting reactions to Armstrong's decision.
Armstrong has said he will contest the 2009 Tour de France, which the Astana team and Contador missed this year because they were not invited by the tour organisers.
© AFP 2008