With 10 matches of the campaign still to be played, the 20-year-old has missed only one league game so far and kept 15 clean sheets in the process.
That has seen him rise to prominence at Fratton Park and cement his place as first choice for the Republic of Ireland national team.
It has also seen the Dubliner attract a host of admirers from both the Premier League and Championship, with many clubs looking to be the next ones to benefit from his presence between the posts.
Unfortunately, it looks increasingly likely that next move will be away from Pompey.
It remains to be seen if it will be a permanent return to parent club City or another loan move, after spending last season at Rochdale.
Regardless, Cowley knows he faces a tough task in replacing Bazunu – a prospect that was rammed home yet again on Saturday, following the keeper’s performance in the goalless draw at Ipswich.
He said: ‘You can’t replace Gavin Bazunu, let me tell you. He’s irreplaceable to us.
‘I already know where he’s going (with his career), but if you need any more evidence then just look at his performance against Ipswich, in what was a really big game for us.
‘Even early on in the game, where we had a difficult way in against Ipswich in front of nearly 30,000 fans, he was the one who broke their press with a fantastic ball to Connor Ogilvie and we went from goal-line to goal-line and created a really good attacking moment.
‘That actually gave us the confidence in the game, and our performance built from there. I thought we had a really good period in the first half.
‘It was created through Gavin, really.
‘When we needed him in the second half, and let's be honest, we didn’t really need him too much.
‘But the one or two times we did, he made some good saves.’
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