The Potters boss declared that David Moyes's side cannot afford any further "slip-ups" if they hope to retain their Premier League crown.
"They can't afford any more slip-ups. Maybe they are a little bit vulnerable," The Mirror quotes him as saying.
"I don't think there's that aura around the club at the moment and maybe it's a good time to meet them.
"There are only a certain amount of games you can lose. Five or six keeps you in the title race. Lose any more and you make it very difficult, nigh on impossible."
Hughes appeared more than 400 times for the Red Devils during his playing career, completing two stints at the club.