Mickelson said he was interested in spending more time in Europe
Ernie Els fears a change in European Tour membership rules could lead to US stars rethinking plans to play more on the other side of the Atlantic.
Big names like Phil Mickelson had hinted at playing more tournaments in Europe in order to qualify for the lucrative Race to Dubai event.
But the European Tour has upped the minimum number of events a player has to take part in to be a member to 12.
"For US guys to change schedules and play here, I don't think so," said Els.
The world number eight, talking ahead of the Dunhill Links Championship at St Andrews, said the European Tour might need to think about exemptions to tempt US players over to Europe.
"Mickelson has indicated he wants to play a bit more around the world, he's bought a new airplane so I think he can put some miles on it," added Els.
"But I don't know if there's going to be special exemptions for players to play in the Race to Dubai. If that's not the case, I don't know if the (American) guys will really change their schedules to that extent."
But Els said golf and the PGA Tour would not be immune from the global credit crunch, and the pressure on sponsors could lead to players altering their plans anyway.
"There are some big questions there with the US economy," he said. "I would think that some of the financial and motor companies might be in a bit of stress."
The four majors and the three World Golf Championship events all count towards European Tour membership, meaning players would have to compete in a further five events to have a chance of qualifying for Dubai.
Els plays on both of golf's principle circuits, and said he expected more players to follow his example.
"I think to raise it to 12 is really not all that much to ask players to do, you can play both tours," said Els.
"A lot of the younger players are doing it now, so it's very do-able."