Simunovic signed in September 2015 aged 21 for a fee reputed to be between £2.5m and £3.5m. He signed a four-year contract in 2017 to keep him at Celtic until 2021.
With suspension against Rosenborg, and Boyata still working his way back to fitness post World Cup, the centre back positions as are once again the subject of debate as seems to be case every season since 2014/15.
In the 2014/15 season only three centre backs were used for more than a handful of games. Ambrose played the equivalent of 34.78 matches, Denayer 42.33 and Van Dijk 56.76.
Since then no centre half has racked up enough minutes to have played 40 matches equivalent, with Boyata (39.56) the closest in 2015/16.
A regular partnership has not been found in central defence. Although Rodgers alternates between a back three and four, that lack of continuity continues today.
Simunovic has been the big ticket signing from the current cadre and is still only 23, a mere 9 months older than Hendry. He remains a player of potential but his time at Celtic has not been trouble free.
49 matches have been lost to injury and 4 to suspension. He has been unavailable for 32% of all Celtic matches since joining. That does not include matches on artificial surfaces upon which he prefers not to play due to knee concerns. In 2018/19 three SPFL clubs have artificial surfaces meaning he could miss up to six fixtures in the league alone.
12 matches in a row is his longest run of appearances since joining – achieved in the 2015/16 season.
Latterly poor discipline and decision making have exacerbated his absence from the squad. Woefully out of form in the 0-4 defeat that brought the invincible run to an end, he has subsequently been sent off in high profile games at Ibrox and at home to Alashkert for needless violent offences.
He remains an asset to the club, but when on the pitch, have his performances improved?
Defensive Action Success Rate (DASR%)
This is my key defensive measure. It compares challenges, interceptions and other defensive actions that have been successful versus unsuccessful to provide an overall ratio.
“Good” is Van Dijk at 81%. For bench marking purposes, Ambrose would be 73%. It’s a narrow band.

The 15/16 season saw only 17 appearances and was over after January 23rd due to a serious knee injury. Yet in those early days, partnered mainly with Boyata, he achieved his best DASR%, pushing up towards 79% (which Ajer achieved last season).
Since then it has been quite a drop down to 74% in the last two seasons.
Possession Won and Lost
Winning back possession whilst not giving it away are core competencies for a defender. This compares defensive actions where possession was won outright versus where possession was given up (losing tackles and aerial challenges outright plus giving the ball away due to miss controls).
Last season Boyata topped this metric wining back possession with 89% of defensive actions. At the other end Hendry scored 77%.

Simunovic achieved one of the highest Possession Win % scores in his first season touching 90%. Overall his scores are in line with the better values across the last four seasons I have data for.
But the overall trend is the same whereby his initial 15/16 season saw the best performances, with a drop in 16/17 and then a small improvement in 17/18.
Defensive Errors
As well as the error strewn game away to Heart of Midlothian and the sendings off mentioned above, Simunovic also had a high-profile error away to Zenit Saint Petersburg losing Ivanovic for the opening goal.

And this is where the stats don’t support what was the prevailing narrative! He committed MORE defensive errors in his first season, and the least in his middle season which by all other measures was his least effective. His more high-profile errors probably came last season where his overall error rate was an average 0.52 per 90m. Which goes to prove it is not necessarily the volume of errors, but do you get punished for them?
Ajer, for example, tends to make errors against the lower SPFL sides but hardly ever in the higher profile matches.
Simunovic’s initial error rate over 1 per 90m is Ambrose-esque. His latter error rates are around the average for Celtic central defenders.
Conclusion
Simunovic’s Celtic career has been characterised by a lack continuity of availability. Early promise was halted in the New Year of 15/16 with a serious knee injury that took until September 2016 to clear. When he has played he generally plays to a good level by the standard of centre backs Celtic have had recently. However, it is a concern that in 16/17 when he played the most minutes (2824) he also posted the least impressive performance stats.
Overall his performance data shows no trend of improvement over the last three seasons.
Recent failures of discipline have compounded this lack of continuity with him being dropped in favour of the Boyata / Ajer partnership.
Continuing absence through either injury or suspension must erode trust that he can be relied upon over a 60+ match season.