McLeish parted company with Forest after just 41 days as manager, leaving the Championship club searching for yet another boss.
And while Al Hasawi admits the task is bigger than he anticipated, he insists he remains committed to bringing success to the City Ground.
He told Forest's official website: "I cannot pretend that the last six months or so have been an easy time, either for myself and my family or the club as a whole.
"We have had to make some difficult decisions and have had many issues to resolve.
"I know that many of our fans are frustrated. I want them to know that I share their frustrations but I remain as committed as ever to Nottingham Forest.
"The challenge is bigger than I envisaged when we purchased the club last summer but I will do everything I can to bring success and happiness back to the followers of Nottingham Forest.
"We have another important decision to make in appointing a new manager and ask for supporters to be patient.
"We have a strong vision and plan for Nottingham Forest and our willingness to succeed remains undimmed by the disappointments we have experienced in the past six months.
"We will return Nottingham Forest to its former glory."