Celtic fans have made it quite clear that they are not happy with how things are being run at Parkhead at the moment. The attendance for their pre-season game against Middlesbrough was a clear indication of that.

It is not hard to see why in the current circumstances. The club struggled throughout the previous campaign despite ultimately winning a last-minute league and cup double.

Since then, the Rangers have continued to invest. On the other hand, Celtic have made only one signing.

On the other hand, they have failed to get deals done for two of their key players from last season, Kelechi Iheanacho and Marcelo Saracchi. And it looks like the squad could be further weakened, with Manchester United's transfer activity acting as a catalyst.

According to a report from Gazzetta dello Sport, Manchester United are in pole position to sign Manu Kone, but Chelsea are also eyeing him. The transfer fee is expected to be in the region of €55 million.

On the other hand, the report from Italy further states that Arne Engels is one of the players being eyed to replace the Frenchman.

Engels has been linked with a move away from Parkhead for quite some time. In fact, there was a £25 million bid to sign him last summer.

While Celtic did reject it back then, they might not if something similar, or even bigger, comes in this summer, which is quite likely judging by the level of interest in the Belgian international.

There has been little positivity around Celtic over the past few months. And things could be about to get worse, if Engels ends up replacing Kone for AS Roma.

AS Roma have been linked with Engels in the past as well, and now, the football math makes sense with the talks of Man Utd wanting Kone.

Replacing Engels won't be an easy task, especially when you take into consideration how Celtic have handled their transfer business lately.

READ MORE: Bad News Confirmed for Celtic

They allowed the option to extend Iheanacho's deal to expire and then lost him. And the failure to sign Saracchi is an even bigger headscratcher, as the finances involved in the deal were not thought to be that high.

It remains to be seen how the club go about it over the coming weeks, and if they are successful in winning over the support, although that is starting to feel a bit unlikely at this point in time.

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