Brighton4 - 0Crawley

The 23-year-old was only unveiled as a new Seagulls signing on Monday, joining the Premier League club from Scottish giants Celtic for a fee which could rise to around £30m.

O'Riley was immediately thrown into Fabian Hurzeler's starting lineup as one of 11 Brighton changes from last weekend's last-gasp 2-1 Premier League win against Manchester United.

However, the midfielder ha his debut ended early by a late, crunching tackle from Crawley captain Jay Williams, and he required lengthy treatment on his left ankle before he was helped off the pitch by a pair of Brighton medics.

Hurzeler was left enraged by the challenge and has since indicated that further assessments must take place to determine the full extent of O'Riley's injury.

Hurzeler: 'O'Riley injury does not look good'

Speaking to reporters after the match, Hurzeler said: "I think after this foul the players could tackle like they want, because there was no yellow card. For me it was a clear red card.

"You can't tackle like this. You can be hard, you can be ruthless, but you can't take the risk to injure a player. He (Williams) was much too late.

"It doesn't look good, to be honest. [O'Riley] said to me he could not put any weight on his ankle, so it's not nice. I hope Matt is not as badly injured as it looks. We have to wait for the scan on his ankle."

Crawley manager Scott Lindsey has since apologised for the tackle by Williams, who was not booked for the initial challenge on O'Riley but received a yellow later in the contest for a different incident and was the subject of persistent boos from the Brighton supporters throughout the evening.

"Maybe we were a bit aggressive, maybe the referee missed it and I would like to apologise," Lindsey told reporters. "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."

Brighton thrash Crawley, but O'Riley is a doubt for Arsenal clash

O'Riley's injury marred what was another positive result and performance from Brighton, who cruised to a 4-0 victory over Crawley in a feisty EFL Cup second-round tie at the Amex Stadium.

Goals from Simon Adingra, Jeremy Sarmiento, Adam Webster and Mark O'Mahony secured Brighton's progression to the third round and preserved Hurzeler's perfect record in charge of the Seagulls.

O'Riley has now emerged as a doubt for Brighton's challenging Premier League clash away against Arsenal at the Emirates Stadium on Saturday.

The Denmark international has joined the Seagulls after ending the 2023-24 campaign as Celtic's Player of the Year and joint-top scorer, netting 19 goals and providing 18 assists in 49 games.

Solly March (knee) is one Brighton player who remains sidelined, but on a positive note, Hurzeler was able to welcome back Pervis Estupinan, Tariq Lamptey and Evan Ferguson to his matchday squad on Tuesday.

Meanwhile, Brighton announced the signing of full-back Ferdi Kadioglu from Fenerbahce prior to kickoff against Crawley and the Turkey international could be available to make his debut against Arsenal.