Defour, 22, has been a long term target for the Red Devils over recent years, with Sir Alex Ferguson sending him a personal letter of motivation to help him get over a broken foot last year.
But with Arsenal and Liverpool also reportedly plotting a swoop for the Belgian international following his return to fitness, Defour could have a dilemma on his hands in the not too distant future.
"I know that Manchester United are closely monitoring my situation. There hasn't been any official contact yet though," Defour told Belgian TV programme Extra Time.
"I've been sidelined for quite a while due to injury, but I'm playing at a high level again. The chance that I'll leave the club is rather big if I continue to play like I currently do.
"I've had the opportunity to leave Standard on more than once occasion in the past couple of seasons, but I loved the club too much to leave. However, I'm 22 years old now and I also have to think about myself.
"There comes a time when you just have to make the next step in your career, regardless of sentiments for any club."
The highly-rated midfielder was being tracked by Arsenal boss Arsene Wenger before his injury in September 2009, while Roy Hodgson is believed to have sent his Liverpool scouts over to watch Defour in action on several occasions this season.
Having recaptured the form that labelled him as one of the best young talents in Europe a few years ago, Defour insists he is close to full fitness, despite still suffering from slight discomfort.
"The pain is much less severe than it was at the beginning of the season. The pain will eventually disappear altogether, but I have to do my exercises every day and work hard."
Ferguson is expected to swoop for Defour in the not-too-distant future, with both Paul Scholes and Ryan Giggs approaching the end of their glittering Old Trafford tenures.
By James Martini
