Paul Dunne has lost his European Tour card after a missed cut at the Portugal Masters saw him finish outside the top 117 in the Race to Dubai rankings.
Dunne, 118th in the standings, carded a second-round 74 to finish four shots outside the cut on three-over par.
Dublin's Gavin Moynihan also lost his card after back pain forced him to withdraw after 16 holes on Friday.
The pair face a trip to Q School in November to try and regain their playing privileges for the 2020 season.
After shooting a level-par 71 in Thursday's opening round, former British Masters champion Dunne started promisingly with two birdies in his opening three holes.
A bogey on the par-four ninth, however, signalled a downturn in his fortunes and he slumped to a damaging eight on the par-five 12th.
He dropped another shot on the par-four 14th and signed for a 74, which dropped him down to 123rd in the rankings.
Greystones native Dunne memorably catapulted himself into the limelight at the 2015 Open Championship when he set the tournament record for the lowest 54-hole score by an amateur to co-lead entering the final round.
The former Walker Cup star captured his maiden European Tour title in style at the 2017 British Masters, where a stunning final-round 61 saw him finish three shots ahead of Rory McIlroy.
But he has struggled to replicate that form this season; his missed cut in Vilamoura is the 12th time he has failed to make the weekend in his last 14 starts.
Moynihan, who entered the week ranked 140th after a career-best tied fifth finish at last week's Open de France, left himself an uphill battle after an opening round 74.
The 25-year-old, who won the GolfSixes event alongside Dunne in 2018, was one-over par for the day before being forced to retire due to back pain.
Ballymoney's Michael Hoey, who has reduced playing privileges after losing his card in 2016, also missed the cut after rounds of 70 and 78 saw him post a six-over par total.