Jussi Jaaskelainen has won a new 12-month deal in the past week.
Allardyce said: "It depends on what is on the market. We have had young (Stephen) Henderson on loan at Ipswich. He has found life very difficult being number two and not playing.
"Having come from Portsmouth where he played every week and now sitting on the bench, he found it mentally tough and we thought it was better that he goes out and plays and poses a bigger challenge to Jussi next season.
"We will find out pre-season and if that doesn't prove to be the case, I will look at it during the summer. If we haven't got enough [cover] I will look at the market and see if we can find the right one."