(CNN) -- McLaren team principal Martin Whitmarsh has questioned the reasons behind Lewis Hamilton's imminent move to Mercedes, suggesting the 2008 world champion's switch is money motivated.
Hamilton announced in September he would be ending his career-long association with McLaren, with Mexico's Sergio Perez set to replace him at the British team.
Whitmarsh claims McLaren, with whom Hamilton made his F1 debut in 2007, put a contract on the table which would have made the Briton the highest paid driver on the grid.
But Hamilton instead opted to join Mercedes on a three-year deal, where he will replace retiring seven-time world champion Michael Schumacher.
"We made Lewis an offer," Whitmarsh told the sport's official website. "An offer, which I believe is more money than any other driver at the moment is being paid.
"That leads us to suspect that our competitor and our partner Mercedes-Benz offered a bit more money. I don't know that, but I think for Lewis [sic] made his decision. I am disappointed in one sense, but you have to focus on going forward."
Hamilton, who reportedly earned $24m this year with McLaren, has endured a frustrating 2012 season.
Despite winning three grands prix, his title challenge has been dented by four retirements in 18 races, leaving him fifth in the drivers' standings with two races of the season remaining.
The news of Hamilton's move came just three months after Whitmarsh had scotched talk of the two parties ending their association.
Hamilton worked his way up through McLaren's young driver program having introduced himself to then team principal Ron Dennis at the age of nine.
"In fairness, if I had said three months ago that Lewis might leave I probably would have made some fantastic headlines, but that wouldn't have been in our interest," explained Whitmarsh.
"The media try to create entertainment from our faux pas. Imagine if I had said Lewis was going to leave. It would have been immensely destabilizing and honestly I didn't think that he was going to leave. I was surprised, but I was not shocked."
Whitmarsh also speculated Hamilton's decision could have been influenced by the Singapore Grand Prix, in which he was forced to retire due to a gearbox problem after starting the race in pole position.
" I am pretty sure he hadn't made up his mind until after Singapore. He told me the Monday or Tuesday after Singapore," continued Whitmarsh.
"I think it is always bad to make a decision in the aftermath of a bad race. He was pretty sure that he was going to win that race and it was a disappointment and as I just said it is never good to make a decision in such a situation."
Hamilton made a huge impact as a rookie in 2007, coming close to clinching the championship title which was eventually won by Ferrari's Kimi Raikkonen, despite continually clashing with teammate Fernando Alonso.
Whitmarsh is hoping McLaren can enjoy more success with an inexperienced driver when Perez joins the team in 2013, having impressed with Sauber since making his F1 debut in 2011.
"Some of the greatest moments in my life I've had when working with Mika (Hakkinen) when he was young. And we won the world championship with Mika," he said.
"And with Lewis, when he was young, so I am excited. It is a risk taking on a young driver. Bear in mind that when we took on Lewis he was the same age as Sergio is today and he was incredibly young, incredibly raw and incredibly talented.
"Now when Sergio gets to Australia in 2013 he will arrive with the kind of pressure that he can't imagine right now."