After a 1-0 home win a fortnight ago through Darren Jackson's goal, Celtic are 90 minutes away from joining Europe's elite. That would rank as an achievement in itself according to Boyd, who believes being part of the Champions' League is the key to restoring the Scots' diminished reputation overseas.
This season has seen the launch of the new Scottish Premier League, but domestic rewards cannot compare in scale to victories over Europe's finest.
At this stage last season Newcastle deprived Zagreb of qualification, and now at the Maksimir Stadium the Croatians are determined to overturn that setback.
However, as Boyd stresses, Celtic's own motivation stands comparisons as they aim to redress the recent failings of Rangers in the same competition. He said: "Just to make the Champions' League, that is you in with the best. We have had a lot of disappointing results in Europe recently and no Scottish club has really gone too far. But we know if we can get a result in this one game, we are then guaranteed at least six matches against quality opposition."
Boyd knows how Celtic approach this return leg will be crucial. An away goal scored first would leave Zagreb needing three to win, and yet while the match remains goalless the emphasis will be on the trailing home side to be the more positive.
Celtic's main injury concerns are Jackie McNamara and Morten Wieghorst. That Wieghorst missed Saturday's 2-1 win over Dundee United effectively rules the Dane out, as his last game was in pre-season against Kilmarnock when he sustained a knee problem.
Jozef Venglos, the head coach, is more optimistic about McNamara, who will be given maximum recovery time because of his importance to the game plan. He said: "There is so little between the teams that one man playing or not playing could be the vital difference, but only those 100 per cent fit can be considered."