The 26-year-old had only just returned from a four-month absence in January after missing most of 2023 with a foot injury that required two surgeries.
Martinez featured off the bench in the 2-2 draw against Tottenham Hotspur before starting the wins against Newport County, Wolves and West Ham.
But he appeared to suffer a knee problem in a tangle with Hammers right-back Vladimir Coufal in the second half of Sunday’s triumph, United’s fifth in seven games.
And after Raphael Varane replaced Martinez for the final 20 minutes, Ten Hag confirmed that he feared the worst, describing the injury as a “personal disaster” for his £57million signing.
United are now awaiting the diagnosis but face going without their first-choice centre-back for an extended period shortly after regaining his services.
Ahead of the West Ham victory, Smith hailed Martinez’s return, paying particular attention to the World Cup winner’s character.
“You look at the personnel – I think having Martinez coming back is great because he looks like a real winner and a leader in the dressing room,” Smith told BritishGambler.co.uk.
“The signing of players personality-wise was something that Sir Alex looked at in-depth, in terms of their character, not just their ability – ability can be measured in many different ways.
“To play for Man United, the scrutiny is still there, regardless of them not winning the Premier League for however many years. It’s still probably the biggest scrutiny in football.
“Manchester United, Real Madrid and Barcelona – they’re probably the three that get scrutinised the most. It takes a certain type of person to embrace that.”
He added: “Martinez carries that intensity and that determination – it might not be different to anybody else, but visually, he always looks like the type of player that would run through a brick wall for you.
“He’s the type of player that a fan can relate to, and that’s what it takes to have a good connection. When you play, all the fans want to see is you doing what they would do in terms of effort and commitment.
“If they see you doing everything possible, you might not be good enough or struggle at times, they’ll forgive you – and that is all Man United fans want to see.”
Ten Hag now joins the fanbase in praying for the best ahead of a crunch period, including trips to Aston Villa, Luton Town and Manchester City.