Rumours are circulating of a possible change of engines for McLaren in 2014, when Formula 1 will move from the current 2.4 litre V8s to 1.6 litre V6 turbos.
It was reported some time ago that Honda might be considering a return to Formula 1 as an engine supplier, and that McLaren were potential customers. The team denied the rumour.
More recently, a switch to PURE engines has been suggested in the media. Again, McLaren have moved to deny the rumour, and the team has stated that it is happy with Mercedes-Benz and intends to continue the current partnership. There would be good reason to do so, given the success of the McLaren-Mercedes pairing over the last two decades.
However, there has been no indication of the length of the contract with Mercedes-Benz, which suggests that change may be possible. Mercedes has its own works team and will want the new Mercedes engine to work well with the Mercedes car. It therefore makes sense for McLaren to find an engine partner who would be more likely to design the engine to suit the McLaren car.
At this point, this is all speculation, but until McLaren makes some sort of definite announcement, the rumours are likely to continue.