Brawn GP chief executive Nick Fry believes Jenson Button is making a mistake by leaving his team for McLaren - and thinks Button will have to 'raise his game' to avoid being beaten by new team-mate Lewis Hamilton.
Just a fortnight ago Ross Brawn was "99 per cent certain" that he would hang on to Button after their stunning title success this year, but as talks dragged on without resolution and McLaren's discussions with Kimi Raikkonen similarly floundered, McLaren pounced to sign the world champion.
Fry said he is struggling to understand why Button has made the switch, and thinks he could be in for a tough time.
"I respect his decision," Fry told Autosport.
"It's not one that I would have made and maybe he has been poorly advised.
"Clearly, loyalty would be nice but in this day and age you don't expect too much of that.
"I'm always happy when any employee leaves our company if I think that they've made the right decision and they are going to a better job and they always go with our blessing if that is the situation.
"In this situation, we don't understand the logic of the decision and I think Jenson is going to have to up his game if he's going to beat Lewis on home territory."
Amid suggestions that Brawn - now owned by Mercedes - was unwilling to meet Button's salary demands even though the champion had taken a voluntary pay cut this year after Honda's exit, Fry insisted that his team would have paid Jenson at least as much.
"We understand that our offer to Jenson may well have been in excess of what he might be getting with McLaren," he said.
"I don't think that it was a financial issue whatsoever.
"It can't have been as simple as that because we believe that our offer was in excess of what he has accepted from McLaren and Jenson has indicated to me personally that may well be the case.
Fry also denied that the Mercedes takeover meant that the team's attention would be diverted towards expected arrival Nico Rosberg to satisfy the new owner's desire for a winning German driver.
"We were a little distressed to read in the press that there were questions over whether the other driver, whoever that would be, would get favoured treatment which we did think was somewhat insulting," said Fry.
Button had been with his previous team since 2003, having joined in the BAR days, and had been regarded as enjoying a particularly close alliance with Fry during that time.