The summer transfer window is upon us and Celtic fans might already be starting to get worried about the situation. The club have not been linked with a whole host of quality players. On the other hand, some of their best look to be heading for the exit door.

That is the reality of life at Celtic Park, to be honest. Every summer, the club end up seeing some of their best head for the exit door. By now, it has become part of the model.

Last year, it was Nicolas Kuhn who joined Como FC. The year before that, it was Matt O'Riley heading to Brighton. The summer before that, Jota had made the move to Al-Ittihad.

So, it should not come as any sort of surprise if more Celtic players are on their way out this summer. And for one, it looks like an exit maybe getting closer.

According to TEAMtalk, Arne Engels is getting closer to leaving Celtic. Crystal Palace are now pushing to get a deal done. Liverpool are said to be plotting a big-money move for Adam Wharton.

One thing is very clear though. Engels is held in the highest regard down in England and the record fee Celtic had paid to sign him might have been a bargain.

Nottingham Forest reportedly view him as the replacement for Elliot Anderson. He is tipped to make a £100 million move to Manchester City this summer.

On the other hand, it looks like West Ham United see Engels as someone who can replace Wharton. A fee in the region of £80 million might be required to sign him.

So, that is the level of talent Engels is being eyes as a replacement for. Also, this might be a great chance for Celtic to shatter that Scottish transfer record.

That figure is currently around the £25 million mark. Celtic already received an offer in that region in the winter for Engels. And they should be at least looking at £30 million, if not more, to sanction a move.

READ MORE: Celtic Looking to Sign Another Japanese Striker

Obviously, it would be tough to replace someone like Engels. He does not always get the credit that he deserves.

But it was after Engels' return from injury that Celtic went on an eight-run to end the season and finish with a league and cup double.

Celtic have been linked with quite a few midfielders lately, which suggests they might be thinking about life after Engels already. One of them is Ivan Basic, currently representing Bosnia & Herzegovina at the World Cup.

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