Lucas is not good enough anymore, he gives away too many silly free kicks and as a midfielder does not carry a goal threat, which you need, a dedicated holding midfielder is not how Klopp plays, he wants all round players who can tackle/create and score goals and interchange positions. I still don't understand how he became a CB ahead of the likes of Klavan, at least it looks like Klopp has stopped that experiment !!!
It's not Lucas's fault Liverpool gave him a big fat contract and didn't try to sell him, it more shows the failings on the management of the club that he was never deemed not good enough.
Only Liverpool could buy a Brazilian midfielder with less technical ability than the English equivalent
I expect Lucas will leave at the end of the transfer Window as we will keep him for cover with the FA Cup replay.