Elon Musk's plan to send robots to Mars might not go as smoothly as he hopes, according to a leading robotics expert.

In an interview with Forbes, Christian Hubicki, head of the Optimal Robotics Laboratory at Florida State University, warned that the billionaire's robots would likely become little more than scrap metal and plastic once left alone on the Red Planet.

“Humanoids fall down. They break. Their code crashes,” Hubicki explained. “Right now, humanoids aren’t reliable enough to be autonomous on Earth, let alone Mars.”

Musk has recently shifted Tesla's focus heavily toward robotics and artificial intelligence.

Last year, the SpaceX founder unveiled Tesla's Robotaxi service, which he has promised investors will increase the company's value by trillions of dollars.

However, the reasonably priced autonomous vehicles reportedly haven't yet proven they can drive safely without human intervention.

Humanoid robots are the other major part of Musk's vision. Tesla's flagship robot is Optimus, and according to Musk, the company plans to build 100,000 units per month by next year.

But, a video demonstration of Optimus shared last month revealed several limitations, including the fact that it took an unusually long time to answer simple questions and glitched mid-sentence. Earlier videos saw the robot being able to poach an egg and dance.

Musk has already incorporated these unproven humanoid robots into his famously ambitious plan to colonise Mars.

In April, he announced that Optimus robots would be sent to Mars aboard his Starship rocket by the end of 2026.

According to his plan, they would explore the planet's surface and prepare the groundwork for human settlement. He's recently restated this goal, and while acknowledging that 'a lot needs to go right,' provided a not-so-distant timeline.

“More likely, first flight without humans in ~3.5 years, next flight ~5.5 years with humans,” Musk posted in August. “Mars city self-sustaining in 20 to 30 years.”

While space agencies like NASA have deployed humanoid robots in space, the circumstances were very different, Hubicki explained to Forbes.

For NASA, the robots were 'only on space stations where humans are already there to fix them.'

“Critically on the [International Space Station], humans are there to help and fix the robot when it inevitably falters,” Hubicki added. “On Mars, there are no humans to rescue it, and replacement parts are a nightmare to ship in.”

Hubicki claimed: “Without a major technological leap in humanoid reliability, an unaccompanied humanoid on Mars wouldn’t be functional for long.”