London - Arsenal left-back Kieran Tierney is facing up to three months out with a dislocated shoulder.
The Scotland international suffered the injury during the Gunners' 3-1 victory over West Ham on Monday.
"Kieran will undergo surgery next week and will rehabilitate for around three months," Arsenal said in a statement on Saturday.
Tierney has suffered an injury ravaged start to his Arsenal career after a £25 million move from Celtic in August.
The 22-year-old did not make his debut until late September due to a hernia operation and has made just five Premier League appearances.
Tierney is now also a doubt for Scotland's Euro 2020 playoffs in March.