The South Africa-born flanker had been told that he had to leave the country despite having been capped eight times for England, after his contract was cancelled by his club Sale following a shoulder injury that forced him to retire. Immigration officials told the 33-year-old Fourie on Tuesday that he can stay in the UK while they consider what steps to take.
Lancaster told a news conference in Leeds: "I'm pleased that I hear over the last 24 hours that some flexibility is going to be shown. I spoke to him only last week - he was a player I signed for Leeds from Rotherham and he was outstanding, he was the best signing I made. He was unbelievable."
He added: "It's massively disappointing he has lost his chance to further his international career and his club career as I thought Sale had made a brilliant signing."
Lancaster said from his talk with Fourie the prospect of returning to South Africa was also "quite attractive" to him".
Fourie, whose 18-month-old son Hendro was born in England, has been in the country for eight years, and also played for Rotherham and Leeds.
A UK Border Agency spokesman said: "We have not curtailed Mr Fourie's visa at this time and he is not required to leave the UK.
"His employment contract with Sale Rugby Club has been terminated and his employer has rightly informed UKBA of this decision. We are considering what action to take next.
"If an individual's circumstances change and they no longer meet the terms of their specific visa they can apply for a visa of a different type. Mr Fourie has been informed of the process and the various options available to him. It is entirely up to him if he chooses to explore any of them further."