The 29-year-old keeper has made just one appearance in the SPL this season and is one of 16 Hibs players whose contracts are set to expire in the summer.
Stack is well aware of the competition for places, with Mark Brown currently in prime position to take the No 1 shirt next season.
Competition at Easter Road also comes in the form of Graeme Smith, with both players facing an important few months to convince Calderwood of their long-term future at the club.
"There are plenty of other lads out of contract, and Graeme Smith is one of them, so it's important for both of us that we make an impression on the gaffer," said Stack in the Daily Record.
"It's very hard to do that from the training ground, so my injury hasn't exactly come at the best of times.
"Come the summer there will be a lot of lads leaving and you just want to be one of those that has an offer on the table."