With their best player potentially leaving for United for the second time in six years, Arsenal fans have attempted to comfort themselves by talking up Mkhitaryan's potential. The Armenian joined United as one of the best performing players in the Bundesliga, but Old Trafford regulars have compared his signing to that of another Dortmund import, Shinji Kagawa. There's no doubting Mkhitaryan's ability, but he hasn't shown he is up to performing consistently well in the Premier League.

Other Arsenal fans have decided instead to play make believe and ponder whether Anthony Martial would be a more suitable candidate in the exchange. Of course, the Frenchman is clearly the superior option, but unlike last summer, there's no chance Mourinho would allow Martial to leave now.

Both players initially struggled to adapt to life under the Portuguese manager, with people blaming Mourinho's supposed inability to bring out the best in attacking players. The only year Eden Hazard has been named the best in the league was while playing for Mourinho, but there are of course examples when forwards have failed to shine for the manager, including Hazard himself the following campaign.

United fans longed for Martial to repeat the form of his debut season, but after missing out on a preseason thanks to France reaching the final of the European Championships and off-field issues in his private life, the Frenchman failed to live up to expectations in 2016-17.

Mkhitaryan's struggles last season were similar -- with Mourinho even leaving him out of the squad for a few months -- as he put in the worst shift in recent memory during United's home defeat against rival Manchester City in September 2016.

However, after Mkhitaryan scored in last season's Europa League final and started this campaign assisting goals every week, there was hope he would turn around his unimpressive start.

Yet, even in that bright opening month of the season, Mkhitaryan was largely an anonymous figure in games before popping up with a brilliant pass or cross to set up a teammate. Quiet performances matter little when you're creating goals that win your team games, but in the months that have followed, you wouldn't know he was on the pitch at times and he no longer has goals or assists to redeem himself.

In contrast, Martial has gone from strength to strength this season. He's three league goals away from matching his return from his first season and has already equaled the number of assists. His 10 goals and nine assists from 31 appearances, 19 of which were made in the starting lineup, is a great return.

"I see a great improvement in the person, in the mood, in the face, in the body language -- if you want just a word, in the happiness," Mourinho said earlier this season. "He's a happy guy, he's working extremely well. He starts matches, he tries to do well. He goes from the bench, even if it's for 10 minutes like in the last match at home, he tries to enjoy and try to give something in these extra minutes. I am very pleased with his attitude overall."

There's no doubt over Martial's future at the club. Allowing the Frenchman, who turned 22 last month, to leave the club in order to secure a deal for Sanchez makes no sense, while letting go of Mkhitaryan, who turns 29 next week, does.

The Armenian's agent, Mino Raiola, has defended the player and claimed that Sanchez is the bargaining chip in Arsenal's bid to sign Mkhitaryan, not the other way around, which appears to be the agent stretching the truth somewhat.

Reports have suggested that Mkhitaryan isn't too keen to leave United for Arsenal, but if his playing time continues to be as limited as it currently is, he may be better off making the move to North London. He has played in just three of United's last 10 league games and only one of those was from the start, with him being substituted after 65 minutes.

At Arsenal, particularly with the hole of Sanchez to fill, Mkhitaryan could certainly hope for more playing time under Arsene Wenger.

As it stands, Mkhitaryan may well stay put or leave for a different club, while Sanchez may hold on until the summer when he would be available on a free transfer. United, City and Chelsea would likely all throw their hats back in the ring, even if Antonio Conte has claimed his club aren't interested this transfer window.

Mourinho won't believe his luck if he manages to offload Mkhitaryan and bring a player of Sanchez's quality in as his replacement, particularly as it seemed a foregone conclusion that the Chilean was heading to rivals City even just a week ago. But you would imagine there are still a few twists and turns in this story yet.