Liverpool manager Jurgen Klopp has expressed his disappointment and regret after failing to include defender Jon Flanagan in the Europa League squad. In the round of 16, the Reds face arch-rivals Manchester United as both legs will be played on 10 and 17 March.

The Merseyside club were given the opportunity to make three changes to their squad and resubmit before the start of the knockout stages of Europe's second-tier club competition. Steven Caulker moved to Anfield from Queens Park Rangers on loan until the end of the season in January.

Danny Ings and Joe Gomez are sidelined with long-term injuries. The former Borussia Dortmund manager included Caulker, Joao Carlos Teixeira and Danny Ward in place of Ings, Gomez and Adam Bogdan.

Flanagan started in his first Premier League fixture after 22 months against Manchester City and Liverpool were able to avenge the Capital One Cup final defeat with a 3-0 league win. The defender, who returned from a long spell on the sidelines, will not feature in the European competition as there were still concerns over his fitness.

"Now we have too many centre-halves. The day before we put the squad list in we didn't have any. Now we have too many and you think: 'My God what have we done?'," Klopp explained, as quoted by the Liverpool Echo.

"That was the thing we had to do at that time. Now we have to get into the next round with the players we have available."

Liverpool travel to Selhurst Park as the Reds take on Crystal Palace in the league tie on 6 March. Flanagan is hoping to start in the second consecutive league fixture in less than a week. However, Klopp claims he is in no hurry to include the defender in the starting lineup and will consult the club's medical staff before taking a decision on playing the full-back.

"He hasn't played two games in four days so I am not sure that we should. We are always in talks with Andy Massey (doctor) and Chris Morgan (physio). If you ask Flanno? (thumbs up). But that's not the best advice!" the Liverpool manager said.

"We just have to stay smart. It was brilliant that he was back the other night but at the end there were missed passes, losing challenges, things like this.

"He's not at 100% but I do not expect him to be. How could he be? We will judge the intensity. We look at him and say yes, no or perhaps."