The 28-year-old shot-stopper was brought into the club from Blackburn in the summer and will start for the team over the course of the next few months after the No.1 was sidelined
The club confirmed on Wednesday that England international Ruddy will be sidelined with a serious thigh injury picked up during the 1-1 draw against Everton at Goodison Park.
The news means Bunn, who was signed in the summer, will step into the team although Hughton is not ruling out the possibility of bringing in another fresh face when the January transfer window reopens.
"Those are the decisions we have to make," he told the Eastern Daily Press.
"Mark is an excellent goalkeeper but it is a tough decision because it is such a big job.
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"The form he was in then, yes, it is a big blow, and that is not taking anything away from Mark, because he will be an excellent goalkeeper for us and that is the reason why we brought him in.
"I feel for John because he is in a very good period in his career at this moment with his international involvement with England, but in Mark we have a very good replacement."