107 days after Neil Lennon resigned from his post, Postecoglou was appointed as Celtic boss last month, following Eddie Howe’s decision to pull out of a move north of the border.
The Australian, who left Japanese side Yokohama F Marinos, said “it doesn’t really bother me” when asked if he had concerns over being second choice.
Postecoglou admitted that the most important thing would be to bring success to Celtic, after their run of nine successive league titles was brought to an end by Rangers last season.
Goals from Albian Ajeti, Owen Moffatt and Odsonne Edouard helped the Bhoys come from behind to win 3-1 against Sheffield Wednesday in their first pre-season friendly on Wednesday.
After Saturday, Celtic will make the short trip across the Severn Bridge to face Bristol City next week, before flying back to Glasgow to take on Preston North End ahead of the first leg of their Champions League second qualifying round tie against FC Midtjylland.
Charlton have ambitions of their own for the 2021-22 campaign, with the Addicks looking to win promotion back to the Championship.
The South East London club finished seventh in League One last season, only missing out on a playoff place on goal difference despite beating third tier winners Hull City on the final day.
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Nigel Adkins was appointed manager in mid-March following Lee Bowyer’s departure to Birmingham City and lost just one of the final 10 games of the campaign (W5 D4), while no League One side conceded fewer goals in that period.
It means that hopes are high at The Valley, particularly because Adkins already has two promotions to the Championship on his CV with Scunthorpe United and Southampton.
Also on Charlton’s pre-season scheduled are fixtures against Dartford, Reading, Crystal Palace and Fulham before they begin the League One season against Sheffield Wednesday on August