The Armenia international secured a switch to Arsenal after Manchester United snapped up Alexis Sanchez as part of the swap deal.
Mkhitaryan struggled to leave a lasting imprint at Manchester United following his move to Old Trafford in a £30m deal from Borussia Dortmund in 2016.
The 29-year-old attacking midfielder won the Europa League and the League Cup during his first season at the 20-time English champions.
Mkhitaryan struggled to tie down a regular starting spot under Jose Mourinho and the Portuguese coach was regularly critical of the playmaker.
Mata, himself, fell foul of Mourinho during his spell at Chelsea FC before his move to Manchester United in 2013.
The Spanish winger sent a message to Arsenal supporters talking up their new signing Mkhitaryan.
“I don’t want to forget to wish the best of luck once again to Henrikh Mkhitaryan, a footballer with great talent and a friend that deserves all the good things that happen to him,” Mata wrote on his personal blog One Hour Behind.
“Enjoy in your new club and see you soon!”
Mkhitaryan scored 13 goals in 63 games in all competitions during a two-season spell at Manchester United.
The Armenian midfielder made two Premier League starts in his last three months at Old Trafford before his move to Arsenal.
The Arsenal signing could make his Gunners debut against Welsh side Swansea City in the Premier League on Tuesday night.
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