Apple is readying a new 15-inch MacBook Pro which will feature a Retina display screen, ultra-thin design and USB 3.0 ports. Sources in the company's supply chain say they have handled prototype components and casings, and that the new laptop is undergoing production test rounds at present.

The claimants, which 9to5Mac calls "trusted sources", have also revealed that the new MacBook will be coming this summer.

It's reported that the casing of the new computer will be similar to that of the existing late 2011 model, but thinner and won't feature the taping synonymous with the MacBook Air (as other reports would have you believe). In addition, 9to5Mac writes that there will be no optical drive on the new Pro, in order to keep the newly svelte waistline.

Another obvious design change, according to the sources, will be a new power button on the keyboard, which replaces the disc eject key. The sides of the prototype unibody casing that is going through testing feature a charging port, two USB ports, two audio in/outs and a battery meter on the left-hand side, two Thunderbolt ports, an SD card slot and another USB port on the right. There's no room, it is said, for an Ethernet port.

Other than "summer", no release date has been touted, but we do know that WWDC12 is coming up in June, so who knows? Could we see a public unveiling then?