The Ecuador winger's outstanding form since returning from a hamstring injury last month has been one of the key factors in United's apparent surge towards the Barclays Premier League title.
The 26-year-old left Wigan for Old Trafford in a £16million deal three years ago and his old club now fear he could return to haunt them as they search for points in their relegation battle.
Martinez, who took charge in the same summer Valencia left, said: "If you speak with anyone who worked with Antonio here, they will tell you what an extraordinary character he is.
"We all know the quality he has got and now he looks a fresh player.
"I think Antonio looks a real threat. He looks really sharp and he is enjoying his football, at his best level.
"It seems as though he has been a key man in every fixture he has played and we are all very happy on one hand, because Antonio left a massive stamp on the football club.
"But on the other hand we hope he has a bit of a day off against us."
History is against Wigan having lost all 14 of their meetings against United, including the 2006 Carling Cup final, since they were promoted to the top flight seven years ago.
Martinez has been in charge for the last five of them, in which his side have conceded 21 goals.
But Martinez is encouraged by recent performances, particularly after winning at Liverpool last month and going down to a controversial last-gasp defeat at Chelsea on Saturday.
He said: "The performances we have had at Anfield and Stamford Bridge this season have got rid of that block.
"Against Manchester United you have to be perfect and we know now we can be perfect against these sides. Mentally we are ready for that.
"We are desperate to test ourselves against them and we are hoping for a bit of luck we have not had over the last few weeks or in the last few games against Manchester United."
Martinez yesterday revealed he received an apology from referees chief Mike Riley following the 2-1 loss at Chelsea.
Both of the Londoners' goals appeared to come from offside positions and Martinez described the performance of an assistant referee as "disgusting".
Martinez said: "He [Riley] just said he understands that at the level of refereeing in this league, they should get that call right.
"I think that is a very honourable way to face mistakes."
The Football Association also confirmed Martinez would not face any action over his post-match comments.