The club released three different strips earlier this month, made by new shirt designers Hummel, but none of those were on display in Croatia.
Instead, the away side sported a red strip with no sponsor.
This confused members of a Rangers support, who wondered why their team were taking to the field in what appeared to be a training top.
Osijek’s blue and white hooped kit would have clashed with both the new home and away tops, but many expected to see the new orange third kit in use for the first time.
While there was no explanation for the decision not to wear the orange kit, the club’s supporter liason officer at least cleared up a couple of other things.
He revealed that the red top, while sometimes used in training, is actually a fourth kit, and that there was no 32Red sponsor on the front because Croatia’s gambling laws forbids bookmakers to be advertised on strips.
Replying to a fan on Twitter, Greg Marshall said: “Sponsorship rules in Croatia - red top is our 4th strip.”