Gillespie feels that Harmison's absence in the first Ashes Test at Cardiff allowed the Australian batsmen to relax.
'There is no doubt that the Australian camp was reasonably happy that Harmison wasn't included in the squad (for Cardiff). They know he can be a big match player and they would have been relieved he wasn't playing,' he said.
Harmison's Durham coach Geoff Cook also believes that the fast bowler has done enough to earn a recall for the second Test.
'He had to thrash himself to get anything out of the wicket, but he always puts the effort in for Durham. He's a tall lad and a world-class bowler, he's got lots of wickets this season at not very many and he's bowling very well,' Cook was quoted as saying by The Times, London.
Geoff Miller, the national selector, had dropped hints last week that the bowler may have a chance to come back in the side.
The 30-year-old Harmison has taken 221 wickets in 61 Tests and his last appearance was in the third Test against the West Indies in Antigua in February. He was dropped after that game due to his on-off relationship with the England selectors in recent times.