LONDON (Guardian) - Roberto Firmino remains doubtful for Liverpool's Europa League quarter-final against Borussia Dortmund on Thursday with the forward yet to fully recover from a hamstring problem.

Firmino has been sidelined by an injury sustained in the last-16 tie at Manchester United on March 17 and failed a late fitness test before the Premier League draw with Tottenham Hotspur on Saturday.

Juergen Klopp will give the Brazilian every opportunity to be involved against the manager's former club and the £29 million (S$56 million) summer signing from Hoffenheim will have a further assessment before the squad's departure for Germany on Wednesday.

The 24-year-old is one of five Liverpool players who are a booking away from a European suspension. Philippe Coutinho, Dejan Lovren, Nathaniel Clyne and Alberto Moreno would also miss the second leg at Anfield next week if booked at the Westfalenstadion.

Dortmund have their own injury concerns before the first leg with the midfielder Ilkay Gundogan yet to return from a foot problem sustained almost one month ago.