Eintracht Frankfurt defender Robin Koch is a big doubt for their Europa League opener against Viktoria Plzen on Thursday. The 28-year-old was absent from full training on Wednesday ahead of the home game in the revamped competition. The 2022 Europa League winners said Koch completed only individual exercises. “Robin has a slight issue with his hip. There’s a big question mark over his involvement,” Frankfurt coach Dino Toppmöller told a news conference. Koch was due to be in the press conference with his coach, but his participation was cancelled and he was replaced by forward Ansgar Knauff. M…