Liverpool midfielder Stefan Bajcetic is facing a lengthy spell out due to a stress problem with an adductor.The 18-year-old has been the breakthrough star this season - a year ago he was playing in the Under-21s - but having earned a regular place in the team he will now be sidelined.Bajcetic has travelled to Madrid for the club's second-leg last-16 tie but will take no part in the quest to overturn a 5-2 deficit."A stress response in his adductor, which is absolutely bad," said manager Jurgen Klopp on the injury. "He doesn't feel a lot but he is now out for I don't know exactly how long."We have to let it settle and we will see when he can come back."Bajcetic's injury leaves Klopp short in midfield as captain Jordan Henderson has not travelled due to illness.