The Mexican striker appeared to catch his studs in the turf, before falling to the ground in serious pain.
United medical staff attended Hernandez during a four minute interruption to the game at Villa Park, before placing his left leg in a splint.
Speaking after the game, boss Alex Ferguson said: "I think he's torn ligaments in his ankle so he could be out for four weeks."
Villa were also hit with an injury concerns of their own, with Shay Given and Jermaine Jenas both crocked.
Boss Alex McLeish said: "I'm not sure but I think Shay had a little tweak in his hamstring. Hopefully it's a grade one (tear) and will heal really quickly.
"As for Jermaine, we don't know, but we think he's had an injury to his Achilles but we will wait until the morning to see."
Aside from the injury to Hernandez, Ferguson was satisfied with the result and especially the performance of goalscorer Phil Jones.
He said: "We deserved a victory. We had great possession but at times we were a bit wasteful with chances in the second half.
"Villa Park is a difficult place to go. Phil Jones is a natural centre-back but he's so versatile he can play in midfield. We've got options where Phil can play."
Jones was pleased to net his first goal for the club after he scored an own goal against Benfica in the UEFA Champions League at Old Trafford last month.
But the 19-year-old is in no rush to determine his role in the side after being praised for his versatility by his manager.
He said: "I'm delighted. I've been getting some stick for not scoring and scoring in the back of my own net in the Champions League was not the best way to open my scoring campaign.
"I'm still young and learning the game and I don't think it matters if I cement a regular spot in the side at the moment as long as I keep playing.
"There's time in the future to cement my place in the side and I'm just happy to play for Manchester United."
United goalkeeper Anders Lindegaard was pleased with the result after taking over from David de Gea.
He said: "It's very important to keep a clean sheet.
"Clean sheets are the goals for a goalkeeper and in 10 games no one will remember how many fantastic saves there's been — they'll remember the clean sheets.
"For my sake I'd rather win 1-0 than 10-1 because I'm a goalkeeper and want my clean sheet.
"I thought we played brilliantly defensively."
United's injury list is growing...
Rafael
Fabio
Berbatov
Anderson
Owen
Cleverley
and now add Hernandez to that list... Not good for the busy Dec and new year period... and Anderson, Owen and Cleverley probably won't play in Dec at all...
The villa turf looked almost perfect, you don't see grass coming off easily. Perhaps the soil was a little too hard? That's why the studs got caught and those injuries to hernandez and given.
I am not too worried of Hernandez injury layoff for a while when Wellbeck is still around and Macheda can be the super sup in the striker's dept, although he is not that match fit. maybe time to play Rooney as the lone striker position, where he scored 33 goals in the 2009/2010 season.
I am more worried that united is unable to kill off games after scoring 1-0 after the city defeat. sure defensively they were more sound these days, but offensively they are unable to get the second goal just in case an opponent score late in the game.
Well, for a frest start, on the looks of this morning, utd are certainly playing with better fluidity and they will only get better. Just hoping for city's form to drop........hahaha. No team can maintain a high standard throughout the season. Next mon will be the battle of the big spenders, chelsea and city.
man u now a 1-0 team.
its not a good sign.
rooney again become so cmi?
I am not too concern with the 1-0s as long as they keep winning in this difficult time and keep themselves close to City and in the top 4, they can get better. Cos what matters currently is not to fall off the pack. Had it not been for these 1-0s, they will probably be behind Chelsea and Arsenal and maybe even Newcastle by now...
The most look down team is Spurs.
They are sitting at 2nd place and no one is bothered about them at all.
At least Newcastle got a mention.
But, Spurs is never covered or mentioned even they won last night.
yeh 1-0 is fine....it shows an ability to keep clean sheets. The way city are playing, they score a lot....at least 3 goals per game? Whether they can maintain that form still remains to be seen. And even if they win the EPL title, no big deal. In the eyes of many, they are just like chelsea, a club suddenly at the top because of cold hard cash. Heck, even swansea can do it if they had a mega rich owner.
yes 1-0 is good as long as its a win and a clean sheet, but then when the opponent scores, it is 1-1 and united need to score 1 more to secure the 3 points, like what happened in the newcastle game. 1-0 is never safe, as you never know until the match is over. just ask Bayern Munich in 1999.
wah that one suay la.....actually can tell that utd's form is picking up.
fergie should not sacrifise Rooney, to play in midfield, left flank etc. he should be deployed as the lone striker and a extra player in midfield. Rooney scored 33 goals in the 2009/2010 season isnt it, in that position after Ronaldo left........
Rooney is getting midfield going as far as I can tell, yesterday was much better. But starving Rooney from his best position just behind the striker is making us suffer.
At least defence looks strong.
We should've got more goals yesterday because Villa was simply horrid.
Actually rooney is often prone to losing the ball and making misplaced passes. He seems to lack concentration many times.
Originally posted by Medicated Oil:The most look down team is Spurs.
They are sitting at 2nd place and no one is bothered about them at all.
At least Newcastle got a mention.
But, Spurs is never covered or mentioned even they won last night.
well, spurs is moving up.. I don't think they are looked down in anyway. Perhaps in the spurs forum, they are blowing smoke and breathing fire over there.
I felt that Rooney is not playing in his natural position ie lone striker or the second striker. behind the striker.
Originally posted by Medicated Oil:The most look down team is Spurs.
They are sitting at 2nd place and no one is bothered about them at all.
At least Newcastle got a mention.
But, Spurs is never covered or mentioned even they won last night.
I don't think Spurs is being 'looked down' on. Actually if you see the table, they are or could be above United so no comparision there. What I was saying is, if not for United's 1-0 wins, United could be worse off by 5, 6 or even 7 points. And those I mentioned are just in that point area. Spurs are of course currently not in that group... They are doing far better.
hernandez has been coming in/out from the injury list
i doubt tonite match
they likely go for a draw instead of a win