McLaren's Jenson Button said Ferrari may have inadvertently given a boost to their rivals by re-hiring former world champion Kimi Raikkonen to join current lead driver Fernando Alonso.

Button, speaking ahead of Sunday's Singapore Grand Prix, said the decision was "great for us" and predicted difficulties at Ferrari as next season progresses.

The 33-year-old Briton said rather than being a dream pairing, two-time world champion Alonso and "Iceman" Raikkonen, who won the 2007 title with Ferrari, may find it difficult to cooperate.

"We'll definitely be watching their situation," Button told AFP.

"Ferrari for many years has had two drivers in the team that have been very quick but when it gets to a point in the season, it seems one driver helps the other driver.

"I don't think that will be the case with Kimi and Fernando -- I don't think they'll be trying to help the other driver. A guy that's achieved what they've achieved will not want to be helping out his team-mate."

Seven-time world champion Michael Schumacher has warned that the partnership could be "explosive", while Red Bull advisor Helmut Marko reportedly said the strong-willed duo could tear the team apart.

Button said Alonso would probably leverage his long personal history within the team to keep staff on his side when Raikkonen arrives from Lotus.

"I'm sure when Kimi walks in that door, Fernando will start talking Italian to all the team personnel. That's exactly what I would do," he said at an ExxonMobil promotional event.

"It's going to be an interesting atmosphere and relationship between those two, especially if Kimi is as quick as Fernando. If Kimi starts out-qualifying Fernando, that will be a big one."

Button has finished second at the past two Singapore races but his best placing in a disastrous season for McLaren, blamed on an over-ambitious new car, is fifth.

He said he would stay with the British team next season by exercising a one-year option on his contract. However, the 2009 world champion is less sure about the outlook for 2015.

"For next year it's all good, it's a formality. Nothing's sorted yet for the year after," he said. "2014 is an option year on the previous contract and then we see. I'm very excited about the future."