Di Maria drought not a concern for Martino
The clash has centred on the head-to-head battle between superstar attackers Lionel Messi and Cristiano Ronaldo - back at his former home in Manchester - but it is the current United number seven Di Maria who will also have keen eyes watching him.
Di Maria has not scored in seven appearances - for club or country - after beginning his United stint with three goals in five Premier League outings.
The former Real Madrid attacker will want to break his run of outs with a goal at Old Trafford, but Martino claimed Di Maria has excuses for his lack of production in recent weeks.
"First and foremost, I'd just have to say that Angel is one of the very top players in world football," Martino said.
"When you're not an expert in the league he plays in, it's hard to make an opinion, but I'll try to talk to you about him.
"I think his start [at United] was exceptional, but I think generally when players go to a new club, and have to get used to a new league, a new team, a different style of football, new team-mates.
"I think the form that he's showing now is a bit more typical of a player going to a new club, in comparison to those very first few games where he burst onto the scene and did so, so well.
"I don't think anything is out of the ordinary with his current form."
Di Maria has been deployed on the left side of United's attack by Louis van Gaal, but Martino claimed it is not the only place the 26-year-old can be influential from.
"As regards whether his current position has any influence, I think that Angel is a player who can play in a number of different roles equally as well," the former Barcelona boss said.
"You only have to look at a few seasons back when he played on the right side for Real Madrid, and then the season just gone he featured more in an inside left slightly more free role, and obviously in the World Cup he did very well when he played wide left.
"I think he's the type of guy who can adapt to anywhere the manager asks him to play."