Guernsey boss Jordan Reynolds said his side played some of their worst rugby for eight years as they lost 28-27 to struggling Tring at Footes Lane.
Guernsey conceded a last-minute converted try to end a three-game winning run in National Three London.
"In the first half we didn't get past second phase, it was ridiculous," Reynolds told BBC Radio Guernsey.
"It was probably the worst I've seen us play in eight years in that first half," added the Guernsey boss.
"Second half we played some really good rugby. But all-in-all we need to have a big gut check and a look at ourselves because we did not turn up for that game."
Guernsey are four points clear of the relegation zone, with games against mid-table Tonbridge Juddians and Westcombe Park still to come.
|Bottom of National Three London & South East|
|12||Amersham & Chiltern||38|
|14||CS Rugby 1863||35|
"The players are going to hate themselves as much as anything I could probably throw in front of them," Reynolds said.
"Tring just really wanted it, they were desperate for it and we just didn't look desperate, so we'll just have to have a discussion and see how we're going to have to go."