Celtic might have won the double last season, but they were near their own sky-high standards. The truth is that the Hoops stumbled over the finish line, and a large part of that success was down to the failure of their title rivals.

Celtic's biggest competition in Scotland is itself. And the club must outdo what they achieved in the previous campaign by a long margin.

There are a number of positions were Celtic must improve in this summer transfer window. One such position is between the posts.

Kasper Schmeichel has retired after a serious injury in the twilight of his career. Viljami Sinisalo did a good job of taking his place in the team in the last few months of the campaign. But is he the long-term number one?

The club have already missed out on one of their targets in that position with Jari de Busser heading to AZ Alkmaar. And unfortunately, it now looks like they are set to miss out on another.

It was just yesterday that news broke that Celtic had taken an interest in Hertha Berlin goalkeeper Tjark Ernst.

The German youth international might still be playing in the second division in Germany might the underlying numbers suggest that he could be a good addition to Celtic. But unfortunately, it looks like that move is no longer on the cards either.

According to WAZ (via Michael Shearer), Wolfsburg have reached an agreement with Hertha Berlin to sign Ernst. The German club are now waiting on the 23-year-old goalkeeper to make his decision.

Celtic and Ajax are believed to hold an interest in the player. But now, it is down to him and whether he would turn down a move to Wolfsburg to join either of those two, or perhaps another different team.

Ernst plays in the second division of German football. That has led many to question whether he would be able to deal with the jump to Celtic.

To be honest, that is a fair question to ask. That being said, it does feel like Ernst has the tools to be a success at any level.

Last season, playing for Hertha Berlin in Bundesliga 2, he faced an xGOT of 52.52 and conceded 44 goals. So, he prevented 8.52 goals.

In comparison, Sinisalo faced an xGOT of 13.35 and conceded 15 times. So, he let more goals in than he should have based on the data.

READ MORE: Celtic Expected to Submit Bid for 22-Year-Old Defender

Ernst also has a 69.2% save percentage, which is significantly better than Sinisalo's 60.5% save percentage.

Ernst's passing could do with a bit more work, as he seems average in that respect. But importantly, he did not make a single error leading to a goal, which means he is reliable with the ball at his feet.

None of this is a criticism of Sinisalo. He played in a different league, under different circumstances. Such data does not always convert on the pitch.

Anyways, if Ernst ends up accepting a move to Wolfsburg, there would not be a comparison to be made.

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