A multitude of complicated footballing and psychological reasons can be used to explain Rangers' slump since the return from the winter break, but there is no doubt that Steven Gerrard's squad lacks the required depth needed to challenge the status quo in Scotland.

On the chalkboard

Rangers' title aspirations were dealt a potentially terminal blow on Wednesday night as Kilmarnock staged a late show to record a 2-1 victory at Rugby Park.

In the absence of Borna Barisic, who was sidelined through injury on the night, Andy Halliday was trusted to deputise at left-back.

Despite being a holding midfielder by trade, he naturally offers more balance than the right-footed Jon Flanagan in the left-back position and it was no surprise to see him included in the starting XI.

The Scotsman may have provided the assist for Scott Arfield's opener, but his defensive frailties were exposed when Stephen O'Donnell was allowed to stab home the equaliser unopposed at the back post.

Distinct lack of depth

Halliday is a functional option at best for Gerrard but the gulf in class between him and Barisic is alarming.

He is far from the standard Rangers need to go all the way in the SPFL, and the fact he is, on current form at least, the most obvious replacement for Barisic underlines the lack of strength in depth which is ultimately holding the title chasing outfit back.

Neil Lennon, by comparison, has Boli Bolingoli and Greg Taylor to choose from at left-back - two options who are levels above Halliday and the incredibly inconsistent Flanagan.

At right-back Gerrard faces a similar problem in the shape of Matt Polster, who is considerably inferior to James Tavernier and struggling to make any sort of impact at Ibrox despite some fleeting glimpses of promise in recent weeks.

Beyond the starting XI there is a lack of quality alternatives at Gerrard's disposal from back to front, and Halliday, who is valued at £450k by Transfermarkt, is a prime example of that season-defining problem for the club.