Hector Bellerin has handed Arsenal another untimely injury headache after being forced off with a knee problem against Chelsea.The Spanish full-back was stretchered from the field with 18 minutes remaining on Saturday.He had gone down unchallenged, with the sight of him crumpling to the turf causing immediate concern. Article continues below Editors’ Picks ‘There is no creativity’ – Can Solskjaer get Man Utd scoring freely again? ‘Everyone legged it on to the pitch!’ – How Foden went from Man City superfan to future superstar Emery out of jail – for now – as brilliant Pepe papers over Arsenal’s cracks What is Manchester United’s ownership situation and how would Kevin Glazer’s sale of shares affect the club? It quickly became apparent that he was in no position to continue as Bellerin was left clutching his knee and was clearly in some discomfort.After being assessed by medical staff, he was taken off with his left leg in a brace.The 23-year-old has already spent time on the sidelines this season with a calf complaint. That ailment kept him out of action over the hectic festive period.Having last figured for Arsenal in a 3-2 defeat at Southampton on December 16, he returned to the Gunners fold against West Ham on January 12.He is now facing up to another stint on the treatment table less than two games into his pursuit of full fitness.Bellerin appeared to suffer his latest setback when changing direction.His leg gave way beneath him and he was left stricken on the Emirates Stadium pitch.Arsenal had established a 2-0 lead in a crunch clash with their London rivals prior to losing Bellerin, with Alexandre Lacazette and Laurent Koscielny on target .They are, however, going to have to tinker with their defensive plans again over the coming weeks.It remains to be seen how long Bellerin will be ruled out for, but the outlook appears bleak.Unai Emery faces another selection poser as a result, with the Arsenal boss having been forced to contend with several injury issues at the back this season.Against Chelsea, he took the decision to introduce Mohamed Elneny.Ainsley Maitland-Niles, who can operate in either full-back berth, was already on the field after coming on in place of Aaron Ramsey. Check out Goal’s Premier League 2019-20 fantasy football podcast for game tips, debate and rivalries.