The Australia coach believes that Harmison and Flintoff having to bowl more overs than is desirable could take its toll before the end of the five Tests in mid September.
Giles has been earmarked for a key role in containing the Australian batsmen and also in allowing the pace attack to take a breather. But the Warwickshire player sent down only 11 overs for 56 runs in the second innings of Australia's 239-run victory at Lord's while Harmison and Flintoff bowled 27 overs apiece.
Buchanan said: "We played Giles reasonably well in the first Test. He didn't bowl a lot of overs whereas in the end Harmison and Flintoff had to bowl 27 overs each in that second innings.
"Giles is a key strategy in their cog of containing but also resting their impact bowlers and therefore, if he is not allowed to do the containing work, it is unlikely he will stay at the crease which means they need to bring back their impact bowlers.
"We didn't necessarily tax Giles too heavily but he was going for around five an over. We understand his role and if we can erode that role, that is going to be pretty important in the context of the whole series, not just now.
"The more that Flintoff and Harmison have to bowl in an innings, the harder it is for them to back up during the course of an innings, then the course of the next innings.
"It doesn't take a lot to work out that the more we can get them bowling and keep them bowling, the better during the course of five Tests in quick succession."Reuse content