The Spaniard insists the Oman international has not been affected by criticism following two errors against Reading and Manchester City and underlined his importance to the team
The 30-year-old's error led to a late Reading equaliser - before Jordi Gomez completed his hat-trick to secure victory for Wigan - while, four days later, Al-Habsi parried Gareth Barry's long-range effort into the path of Mario Balotelli to allow the striker to put Manchester City ahead.
Despite the two blunders, Martinez believes the criticism directed at the shot-stopper has been harsh but insists his first-choice goalkeeper is not affected by the negative comments over his performances.
"I don't think it was an error against Manchester City. Ali in my eyes is one of the best in this league," Martinez told reporters.
"Sometimes you expect Ali to save the unstoppable and that's very unfair.
"Ali is such a confident player and internally he is a very strong human being. I would say his mental strength is his biggest quality.
"As a goalkeeper you need to be able to move on from action to action and he is not affected by that. It's not a confidence issue at all."