McKinna explained: "Last week he did a bit of all right and then today when he came on he made a couple of point-blank saves.
"He's been fantastic. He's training hard, he's keen, he's a pleasure to work with and today he showed again that he's still got it.
"We're not looking at Mark for the season, we're looking at the five-game gap when Danny (Vukovic) is suspended."
McKinna believes Bosnich is enjoying the quieter life of Terrigal but suspects European sides will come calling sooner rather than later - and does not expect to be able to hold on to the player in the long term.
He added: "We're a very small club. If he keeps doing okay, there's no reason why he can't (get back to Europe). And maybe that's the platform Mark is looking for.
"When the transfer window opens up over there opportunities are going to arise.
"If he is playing and playing well here, the games are televised over there and people are going to see he's keen and has his head switched on."
