TO those Celtic supporters who may be wondering, the names are Jeffrey Bruma, Stefan de Vrij, Bruno Martins Indi and Ron Vlaar.

A PSV man, two from Feyenoord and one from Aston Villa. Those are the four centre-halves selected by the Netherlands manager Louis van Gaal for the friendlies his team are about to play against Japan and Colombia. What a talented quartet they must be, if a judge as shrewd as van Gaal rates them above Virgil van Dijk.

If there is a mystery about this increasingly impressive 22-year-old it's not that he remains uncapped, but that Celtic were able to sign him in the first place. Playing for Groningen in the Eredivisie does not amount to obscurity. Van Dijk would have been thoroughly scouted by the heavyweights of the English, German, Spanish, Italian and French leagues.

What was it that made them hesitant or reluctant about making a bid? Whatever flaws were detected have not been immediately apparent in Scottish football. Van Dijk did look oddly unimpressive when going for headers in the opposition's penalty area, tending to make soft connections which sent good chances wide. Even that minor quibble was removed at Dingwall, though. He scored the first two goals, both with his head, in Celtic's comfortable win.

Neil Lennon had done some training ground work with him on the timing of his headers. "My attacking headers have to be better, defensively I don't think I have any problems but the attacking can improve," van Dijk said later. "I had a couple of chances before my first goal. Finally I got my first two goals so I'm very happy about that. I have scored two in a game before. But I've been waiting for my first Celtic goal for a long time."

None of the four centre-halves picked by van Gaal are playing in the Champions League this season, but each has played a few times for Holland before. Bruma, de Vrij and Martins Indi are all 21, younger than van Dijk. The Celtic man's omission from the squad for these friendlies is disheartening because if van Gaal is disinclined to take a look at him now, it's less likely that he will do so closer to the World Cup finals next summer. Despite again displaying his strength, athleticism, composure and pace in the Champions League double-header against Ajax, and being watched by van Gaal's scouts, van Dijk said he will merely "go on vacation, relax, take a rest" during this week's international break. "I want to be in the squad of course but it's not possible just now so I keep focused on Celtic," he said.

"I am still working [to improve]. I think I am playing the best football of my career. I have made progress of course, I have played at the highest level in the Champions League so you learn in every game. My personal performance in Amsterdam was okay but I'm a winner and I want to win every game."

In Dingwall he again looked like a thoroughbred going over the gallops. By the 55th minute he had four headed chances and scored two of them. When Joe Ledley then scored another couple of headers County had completed a hopeless defensive performance which will guarantee a week of self-examination in training. "It was frustrating to concede four headers," said their centre-half, Scott Boyd. "We were compact, so to lose goals from set-pieces was disappointing. We had countered a lot of Celtic's play and kept our shape. To concede goals like that was frustrating."

Lennon's irritation about having to play in the Highlands at Saturday lunchtime, so soon after the midweek game in Amsterdam, was a position he will maintain regardless of the fact Celtic's performance showed no sign of impairment. Had it not been for County's inability to deal with crosses they would have faced a more strenuous afternoon.

For most of the first half they looked unlikely to score. Teemu Pukki spent the game with his back to goal and worked hard to little effect. Young right-back Darnell Fisher got plenty of attention from County, three of whose players were booked for fouls on him. Fisher, Charlie Mulgrew and Emilio Izaguirre delivered the good crosses which gave van Dijk and Ledley their goals.

County were unbeaten in three visits by Celtic last season but went down too easily in the second half this time. Manager Derek Adams is a perfectionist but afterwards spoke like a man who could live with the fact they had been comfortably beaten by a superior team. The wider issue for him is that Celtic are not the only team finding a way through his back four. No side has played fewer Premiership games than County, yet the 23 goals they've conceded is the highest total in the division.