London-born Denmark international O'Riley signed a five-year contract until June 2029 at Brighton
Brighton manager Fabian Hurzeler criticised a "ridiculous foul" which he said should not be "part of football" after new signing Matt O'Riley limped out of the Seagulls' Carabao Cup win over Crawley.
O'Riley, who only joined for £25m from Celtic 24 hours earlier, had his debut ended by a late, crunching tackle by Crawley captain Jay Williams in the sixth minute.
After lengthy treatment, the Denmark international midfielder had to be helped by two physios as he limped from the field.
Hurzeler said the left ankle injury "does not look good".
"You can’t tackle like this," said the German.
"It is a tackle where you take a risk of an injury of another player."
Williams was not booked for that challenge. He was booed throughout the first half and again when he was substituted in the second half.
League One Crawley also had substitute Jack Roles sent off for a challenge on Yasin Ayari in the 91st minute while Hurzeler and Crawley manager Scott Lindsey were both booked by the referee late on.
Lindsey apologised for Williams' tackle after full-time.
"Maybe we were a bit aggressive, maybe the referee missed it and I would like to apologise," he said.
"I wouldn't want anyone to be hurt. We are both passionate about the game and we wish Brighton all the best in the next round."
The win, which secured Brighton's progression to the third round and maintained Hurzeler's 100% record in charge of the Seagulls, came courtesy of goals from Simon Adingra, Jeremy Sarmiento, Adam Webster and Mark O'Mahony.
Brighton come through feisty tie
O’Riley was handed his debut as one of 11 changes as Hurzeler changed his entire XI from Saturday’s late win against Manchester United.
Williams' challenge seemed to interrupt Brighton's flow, resulting in a feisty encounter between the two Sussex-based clubs.
Speaking to Sky Sports, Hurzeler added: "Ridiculous foul.
"It had nothing to do with football. It changed the game because afterwards it got very emotional."
The Seagulls spent much of the first half on the back foot with Ronan Darcy netting for Crawley only to be flagged offside.
The visitors created further chances, the best falling to Josh Flint when he drove in behind from defence but the centre-back’s effort was saved.
Moments later Adingra met Carlos Baleba’s through ball as he ran in off the left and coolly finished for his second goal of the season.
Ecuador winger Sarmiento effectively settled the match three minutes into the second half by firing high into the net for his first Brighton goal after Julio Enciso’s clever turn and driving run.
Crawley created further chances after falling behind but failed to capitalise on clear openings.
With six minutes to play Webster headed in from a corner to seal the win and 19-year-old Republic of Ireland Under-21 international O'Mahony swept in the fourth after winning the ball high up the field - the strike also his first Brighton goal.
Before kick-off, Turkey international Ferdi Kadioglu was introduced to the home crowd having signed in a £25m deal from Fenerbahce but O'Riley's injury soured the evening somewhat.
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