Montgomerie lasted just nine holes of his second round at Sahalee Country Club before calling it a day.

He was four over par and joint 66th of the 78 players when he withdrew.

His failure to shake off his back trouble will be a major concern to European Ryder Cup captain Sam Torrance with just a month to go to the clash with the USA at The Belfry.

"I'm very disappointed. It's a real pity because I was looking forward to coming here and competing," said Montgomerie.

"My back has been causing problems all week and if you compete with others who are physically fit then there is no point carrying on.

"I'm now in the process of trying to get a flight home and I will take stock of the situation after that."

Montgomerie withdrew from the English Open at the Forest of Arden in June last year when back trouble flared up.

He also pulled out of the Johnnie Walker Classic in Perth at the start of this season.