Matasi has been dropped from the squad ahead of Kenya's pivotal AFCON qualifiers.
Kenya's next matches, against Zimbabwe and Namibia, will be held in South Africa, where they must secure victories and hope for favourable results elsewhere to advance to next year's tournament in Morocco.
Coach Firat, who announced his squad this week, selected Farouk Shikalo from KCB to replace Matasi, whose recent performance had come under scrutiny.
Matasi's costly mistakes contributed to Kenya's heavy 4-0 defeat to Cameroon, after which he was replaced by Bryne Omondi for a subsequent 1-0 loss.
"I believe he (Firat) made the right decision to drop Patrick (Matasi), we all know what he has been doing when given the opportunity to play and the two matches (against Zimbabwe and Namibia) need a focused goalkeeper if Kenya are to get something positive in their quest to qualify," Onsika told Flashscore.
"You cannot be letting your team down whenever you start in a game, Matasi has been catastrophic, to say the least, and no one can trust him anymore. Remember Kenya needs to win both matches to stand a chance of qualifying for the AFCON and I think Firat's decision is a brave one, he ought to have done it a long time ago but even now it is a good time to try other keepers."
Alongside Shikalo, Firat has included Omondi from Bandari and Ian Otieno, who plays for Richards Bay in South Africa, as the other goalkeeping options.
As Kenya prepares for these high-stakes matches, Onsika has praised Firat's strategic decision to prioritise fresh talent in the squad, reflecting his belief that a solid defensive unit could bolster Kenya's chances of progressing in the tournament.
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