Fraser Forster returned to Newcastle at the end of last season following a successful loan spell at Parkhead, and the club's very public quest to bring in another keeper has cast doubt on the confidence manager Neil Lennon has in the Pole, who had a comfortable game in the opening SPL win over Hibernian.
Trialist Stipe Pletikosa is already pencilled in to play against Wolves in tomorrow's friendly at Parkhead – as he did last week in the challenge match against Cardiff – but Mjallby bristled at the suggestion that Zaluska is minding the goal until someone better arrives.
The Celtic assistant manager – who confirmed that South African striker Katlego Mphela and Slovakian striker Milos Lacny are also on trial this week and could perhaps feature against the Molineux men – said: "Who said he is not good enough to be No.1? We want to have really good competition.
"Remember last year we had Fraser Forster who broke the record for clean sheets.
"We want someone who is as good as Fraser if we can't have him, so there is competition.
"Right now Lukasz is the No.1 and we have to wait and see if we can bring in someone else who can give him good enough competition.
"We are always on the look out for quality players."
Mjallby revealed he had not been asked for any advice on how to beat Rangers in tonight's Champions League first-leg qualifier at Ibrox by Malmo coach Rikard Norling, whom he played with as teenager in Sweden.
Celtic's Swedish legend Henrik Larsson has spoken to Norling about the Ibrox men but Mjallby – "a born and bred AIK player" – does not expect a call.
"I know their manager but he hasn't spoken to me and Henrik Larsson's word is as good as mine anyway," he said.
"But Rangers are crystal clear favourites to go through."
Mjallby is looking forward to taking on Wolves in the first of four challenge matches before the club resume their SPL campaign at Aberdeen in just under a fortnight's time.
"We want to show the people down south that we are good enough to compete with these clubs," he said. "When I was a player it was really important for us."