Motherwell will be due a compensation fee of around £300,000.

Sturm managing director Andreas Schicker said he "has already proven in Scotland what great qualities he has".

"With his expansive style of play, he gives us another component in the full-back position and will thus positively fuel competition," he told his club website. "Max will have the time to internalise our game principles - we are convinced that he will bring a lot of joy to the fans in Graz."

Before leaving Scotland, Johnston told Sky Sports that it felt "crazy" to be joining a club who are in this season's Champions League qualifiers just seven months after he returned to Motherwell following a loan spell with Cove Rangers in his country's second tier.

He told Sturm's website that he is "happy to be here in Graz and to be able to play in the strong Austrian league".

"I had great conversations with Andreas Schicker and coach Christian Ilzer and I'm absolutely convinced that I'm in the right place here," he added.