It would be a huge coup for Manchester United if they snatch Alexis Sanchez from under Manchester City's nose, because they know Blues boss Pep Guardiola has been chasing him for a while now.

United's interest in the Arsenal forward came out of the blue when it was reported a few days ago but, from listening to their manager Jose Mourinho's news conference on Friday, it does sound like they have made a move for him and I can understand why.

Mourinho said he does not like to speak about other club's players, but then described Sanchez as "phenomenal", so it would definitely appear he wants him.

I would still be surprised if Sanchez ends up at Old Trafford, though, because since last summer it has seemed like he would be joining City at some point.

Sanchez almost joined City for about £55m on the final day of the summer transfer window, only for the switch to collapse when Arsenal failed to sign Monaco and France midfielder Thomas Lemar

Now that move is apparently in doubt because City will not meet Arsenal's asking price but, if Sanchez does still want to go to Etihad Stadium, then he will, because he holds all the cards now.

Even if the Gunners do not agree a fee with City this month, then he can go there for free when his contract ends in the summer. Sanchez only has to sit tight for another four or five months for that to happen.

Arsenal might bench him and not play him if he stays against their wishes, so it would be a pretty miserable time for him, but Chile are not at this summer's World Cup finals so he does not need games in the same way some top players do.

It will be his decision and, whether he ends up at City or United, it will have nothing to do with finances for him because, wherever he goes, he is going to be a very wealthy man.

City are exciting everyone at the moment

I don't know what Sanchez is thinking but my guess - and it is a guess - is that he will choose City.

There are some pretty obvious reasons why Sanchez would want to go to the Etihad Stadium.

He knows Guardiola from their time together at Barcelona and he also knows he would be joining the best team in the country, with the chance of winning lots of trophies this season and in the future too.

Despite Sunday's defeat at Liverpool they are still the team that are exciting everyone at the moment. There is no doubt they are on the up, and it looks like they are going to be there for a while.

Also, at 29, Sanchez is no spring chicken. He has probably got another three or four years at the highest level which, looking at it logically, is also when this City side will be at their peak.

Sanchez would walk into the United team

Mourinho won the Europa League and League Cup in his first season as United manager, and also secured the Community Shield

United are an attractive proposition too, of course.

Guardiola might be having the greater impact at the moment but Mourinho is still a top manager, and also has a fantastic record wherever he has been.

So Sanchez would still have a good chance of success at United, and he would also walk straight into their team.

While he would improve City's squad, he would not be an automatic choice there. He would be rotated and would not play every week, or certainly not as often as he would at United.

I don't think that is a reason for him not to join City, though, because they are still in with a chance of winning four competitions this season, and he would definitely get enough games.

We don't know exactly who he would replace at City when everyone is fit, because they have got so many options, and he could fit in anywhere along their frontline.

But Guardiola wants him now not just because he will fit into the way City play, but because he is eligible to play in the Champions League and FA Cup as well as the Premier League.

City have only lost two out of 34 games in all competitions this season, and have won 30 of them - including two by penalty shootouts in the Carabao Cup

How have Arsenal allowed this to happen?

United are supposedly willing to pay £35m for a player who has only got a few months left on his contract, which might seem a lot when they could get him for nothing in the summer.

But a player of his class with 18 months left on his contract would go for about £80-90m nowadays so it would still be decent business from their point of view.

It is staggering that Arsenal have allowed a situation like this to develop.

For months we have been listening to Gunners manager Arsene Wenger saying that they hope to keep Sanchez and, while we don't know what has been happening internally, from the outside it appears it has never been likely that he will stay.

If a player gets to the last five months of his contract then it appears pretty certain that he will leave - Sanchez could even sign a pre-contract with another club now, and join them in the summer, if he wanted to.

For Sanchez not to play against Bournemouth on Sunday, and also be left out of their FA Cup defeat by Nottingham Forest last weekend, indicates something might be about to happen soon.

If not, then he might have to see his contract out but, one way or another, it looks like he is leaving and Arsenal only have themselves to blame.

In recent years, a top-four finish has always been good enough for Arsenal under Wenger because, financially, qualifying for the Champions League has always been acceptable for them.

But it is looking increasingly likely that they won't make the top four again this year, and they are also about to lose out on a lot of money because they have allowed players' contracts to run down too.

They could lose Mesut Ozil and Jack Wilshere for nothing in the summer and, even if they get £20-30m for Sanchez then that is all they will see out of the thick end of £150m-worth of players.

Then they have to replace them - and they would have to spend another £150m doing that.

So for all the great work that Wenger has done for them financially over the years, they are about to miss out on an absolute fortune this year.

They are the real losers here, not whoever misses out on Sanchez out of City or United.

These are worrying times for the Gunners because they are already miles behind both Manchester teams and it looks like they will be getting weaker, not stronger, in the near future.

Alan Shearer was speaking to BBC Sport's Chris Bevan.