Di Maria was caught on the top of his right foot by a challenge from Portugal counterpart Nani - who is on loan from United at Sporting Lisbon - during the first half of Tuesday's match at Old Trafford
The £59.7million summer signing from Real Madrid required treatment but was able to continue before being replaced around the hour-mark.
Martino revealed that Di Maria had gone for scans but he also allayed any fears the injury might be a serious one.
He said: "We don't think it is anything serious. It was quite a tough blow that he took.
"It was a tough knock. It cut the skin a little bit but we have had a look at it and we are evaluating the situation.
"We are having a look at some X-rays, some images that have been taken but in spite of that we don't think it is too serious."
The contest was billed pre-match as a must-see showdown between Ballon d'Or rivals Lionel Messi and Cristiano Ronaldo, the Argentina and Portugal captains respectively.
There was also hype around the fact ex-Manchester United man Ronaldo was making his return to his old ground, while there were plenty of other Barclays Premier League stars of the past and present on display as well to add to the interest.
In the end, though, the entire spectacle was something of a disappointment, with the Messi-Ronaldo aspect only lasting until half time, when both players were taken off, and the game overall being a stalemate of few chances until Portugal substitute Raphael Guerreiro snatched victory for his side with a header in the dying seconds.
While Ronaldo struggled to make much of an impression, Messi did show plenty of endeavour while on the pitch and hit the post with a shot early on.
Argentina were certainly the better side over the 90 minutes, and asked if he thought the result had been fair, Martino said: "If I'm being honest, I would say no.
"I think over both halves we ran the game, had a lot of possession, created the most chances and I think we were only under threat on two occasions.
"We lost the game and sometimes the result can change your morale and state of mind afterwards
But you can't take away from the fact that, in spite of the scoreline, we put in a good performance."
Then asked if it had been pre-arranged that Messi and Ronaldo would exit at the interval, Martino said: "I wouldn't have the slightest idea about Ronaldo, but certainly we had planned to take off Lionel at half-time - he played the full 90 minutes against Croatia (in a friendly last week), so we decided he would only play 45 here."
Source: PA