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Jurgen Klopp admits he regrets the decision not to include Jon Flanagan in Liverpool’s Europa League squad.

The popular full-back isn’t eligible to face Manchester United in the last 16 next Thursday because he was overlooked when the Reds re-submitted their list prior to the knockout stages getting underway last month.

Liverpool were permitted to make three changes and Klopp opted to bring in Steven Caulker, Joao Carlos Teixeira and Danny Ward for Joe Gomez, Danny Ings and Adam Bogdan.

The inclusion of Caulker rather than Flanagan, who had just returned to action after a long-term knee injury, was questioned at the time. Klopp insisted at the time that with Martin Skrtel having suffered a setback, he needed on-loan Caulker as defensive cover.

However, with Skrtel having since proved his fitness and Dejan Lovren back from a hamstring problem, Liverpool find themselves with five fit centre-backs but with Flanagan, who shone in this week’s 3-0 rout of Manchester City, unavailable.

“Now we have too many centre-halves,” admitted Klopp.

“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?’

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“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.”

Flanagan is desperate to keep his place for Sunday’s Premier League trip to Crystal Palace but Klopp says he must take advice from club medical staff.

He’s wary about demanding too much too soon from Flanagan, who made his comeback in January after an 18-month injury battle, and may recall Alberto Moreno with Nathaniel Clyne reverting to right-back.

“He hasn’t played two games in four days so I am not sure that we should,” Klopp added.

“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!

“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.”