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Liverpool's own young midfielder Jonjo Shelvey is the fifth and final option.
Shelvey is already almost assured of playing some part for Liverpool this season at least, after impressing late last term in an under-performing side and taking his total Reds appearances to over the 30 mark.
A fine performance and goal against Chelsea in particular was memorable for the dynamic 20-year-old.
At present he is arguably the Reds' fifth choice central midfielder after Lucas, Joe Allen, Steven Gerrard and Jordan Henderson, but ahead of Jay Spearing and Charlie Adam.
Bringing in an additional player such as Sahin would almost certainly see the latter two names leave the club, or at least be regarded as immediately dispensable, but would also knock Shelvey back to sixth choice.
With the Reds deploying three of those in every game, six is certainly the number they need for four competitions, but Shelvey has proven over the past few months, and especially in preseason, that he is up for the challenge and ready to showcase his Premier League-level ability as often as possible.
His tenacious tackling needs to be reigned in somewhat as he can be over-zealous in his desire to win back possession, but his hunger and energy are exactly what Liverpool need in midfield allied to the passing, control and technique which needs to come as standard in all Reds from this point onwards.
Capable of playing as a true central midfielder or a more advanced player to break into the box, Shelvey has a genuine chance of making himself an important player for Liverpool this season if given a chance.
If he is given opportunity to shine by Rodgers, expect him to be full of fire—and he could end up saving the club a lot of money in the transfer market.