The Scots were beaten 3-1 in last night's friendly.
Liverpool fullback Robertson told BBC Scotland: "I think we all know that's nowhere near good enough. I don't want to say too much - we need to digest this and speak in the changing room before we start doing interviews.
"But I think we were too easily played through - any chance they had, they scored. We weren't good enough on the ball. We created chances but didn't take them. We were just nowhere near good enough. I don't think you can put a finger on one thing but we need to get it right pretty quickly."
Scotland coach Steve Clarke, meanwhile, insisted on the positives: "We made their goalkeeper work a few times - on another night maybe you get those finishes and it would be a different story. In two days time we're going to Liechtenstein so hopefully we'll get a performance."