Arsenal have reportedly been keeping tabs on promising Celtic midfielder Matt O'Riley since his academy days in London.O'Riley joined the Hoops from Milton Keynes Dons for around £1.5 million in January this year. He has recently turned a lot of heads with his dynamic performances at the centre of the park.A skilful operator with an eye for a pass, the 21-year-old came through the ranks of Fulham before leaving in the summer of 2020. After spending six months as a free agent, he secured a move to MK Dons, where he registered ten goals and eight assists in 54 appearances across competitions. A year later, Celtic snapped him up.Since arriving in Scotland, O'Riley has become a crucial part of Ange Postecoglou's side. He helped them win the 2021-22 Scottish Premiership, contributing four goals and two assists, playing only half the season.Matt O'Riley@mattoriley8Champs baby19438933Champs baby💚 https://t.co/7SaW3b73lqSpeaking to Give Me Sport, transfer insider Dean Jones said that O'Riley has been on Arsenal's radar for several years. He said:"O'Riley is someone who has been on their watchlist for years. Since he was coming through at Fulham, he was a player they were keeping tabs on. To varying degrees, he hadn't quite lived up to his billing at that point."He added:"At MK Dons and Celtic, he has displayed some traits that could show he is a top talent, and there has always been a few clubs sniffing around for him."Earlier this summer, Arsenal were in a race to acquire O'Riley, along with Liverpool, Manchester United and Borussia Dortmund, as per ESPN. Celtic reportedly value the player at £20 million.During the ongoing campaign, O'Riley has elevated his game to another level. The Denmark U21 international has contributed five assists in six league games so far. SPFL@spflA derby goal to remember 🥰O'Riley Jota #cinchPrem | @CelticFC3668315A derby goal to remember 🥰O'Riley ➡️ Jota 🍟#cinchPrem | @CelticFC https://t.co/qihD4KGa4WO'Riley is expected to feature in Celtic's UEFA Champions League Group F opener against Real Madrid on Tuesday (September 6).Arsenal failed to lure Brazilian midfielder Douglas Luiz away from Villa ParkAccording to transfer expert Fabrizio Romano, Arsenal made a late effort to sign Aston Villa midfielder Douglas Luiz on deadline day of the recently concluded summer transfer window. He said:"They tried until the end to sign Douglas Luiz from Aston Villa. But Aston Villa said no to £25 million plus add-ons. They wanted to keep the player."Romano added:"And now Douglas Luiz is staying; he's out of contract next summer, so keep an eye on him because the feeling is that around January, many top clubs will jump into it to sign him as a free agent."Arsenal will open their UEFA Europa League campaign at FC Zurich on Thursday.