WHEN Filip Helander was signed by Rangers last summer, the £3.5million that the Ibrox club shelled out on the Swede was their greatest outlay for a single player in years. The deal to bring Ryan Kent to Govan on deadline day would comfortably eclipse that figure but Helander's hefty price tag brought expectation with it.

Helander's expensive acquisition implied that Steven Gerrard believed that it was Rangers' defence that led to their ultimately unsuccessful title tilt last season, and perhaps there is some truth to this. After all, Gerrard's side outscored Celtic last term but conceded seven more goals and, in the end, finished nine points behind their rivals.

Halfway through his first season in Glasgow, it's fair to say that the jury is still out on Helander. Injuries have disrupted the 26-year-old's debut campaign in Scotland but on the occasions that he has had an extended run in the team, he has given a fairly good account of himself. There has been the odd error here and there but then, no-one is perfect.

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When the centre-half has been sidelined through injury, more often than not Nikola Katic has been filling in alongside Connor Goldson - and the Croatian has generally performed admirably. So much so, in fact, that Helander's place in Gerrard's starting XI might just be under threat despite the great expense it required to bring him to Ibrox.

A quick look at how the Rangers defence has performed with each of the defenders in the team would imply that Helander is the marginally better option. In 16 games in all competitions, the Swedish centre-back has accrued nine clean sheets while conceding a total of 10 goals. Katic, meanwhile, has played 17 games, kept eight clean sheets and conceded 11 goals.

However, when we dig a little deeper into the two players' stats from this season, we can see that Gerrard has two distinctive options available to him to partner the virtually ever-present Goldson in the Rangers backline.

Between the pair, the numbers suggest that Katic is the more natural defender and is the better ball-winner. Helander attempts more defensive duels per 90 minutes than Katic, but the Croatian has a higher success rate. The two centre-backs have virtually identical success rates in aerial duels, but Katic (5.2) has the edge over Helander (4.3) when it comes to interceptions completed per match. Additionally, Helander concedes marginally more fouls per game.

On the ball, however, it is a different story. The two defenders complete roughly the same number of passes per game (around 47) and while Katic's passing accuracy of 88 percent is good, Helander's 92 percent is superb. It comes as no surprise to learn, then, that that Helander gives the ball away on fewer occasions than Katic on average.

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What these stats show is that there isn't all that much separating the two centre-halves but each have their strengths that make them suited to particular opponents. In matches where Gerrard expects his side to be under the cosh against dangerous opponents - such as in Europe or against Celtic - then Katic should get the nod over Helander due to his superior fundamental defensive attributes.

But in matches where ball retention takes priority - against a particularly counter-attacking team or in games where there is a tactical advantage to be gained from exerting control over proceedings - then Helander is the clear choice.

It is a happy dilemma facing Gerrard. Goldson's spot in the starting line-up is evidently guaranteed which leaves just one place for Katic and Helander to fight it out for. Both are enjoying fairly good seasons but it is their distinct styles that will be of the greatest benefit to the Rangers boss; having two different options gives Gerrard a degree of tactical flexibility that his side were perhaps lacking last season, and which could prove decisive in the club's long wait for a top-flight title.