Keller expects want-away Luka Modric to get his way eventually, which would merely confirm his old club's status as sellers.
"Spurs have had this problem for years," Keller said.
"Maybe Arsenal are a little bit different but their fans are upset about that. If you want to be one of the big boys you have to act like it."
During his three seasons at White Hart Lane in the early 1990s, the 41-year-old got used to star men being sold on.
"Your best players should want to stay," he said.
"They should not want to leave because they know they are going to be challenging for trophies.
"Tottenham have to reach that stage. At some point they must make a decision.
"Are they going to honestly and truly compete with these teams or are they just going to hope it all comes together at the right time and challenge for a year or two."