The England midfielder pulled up with the injury in training yesterday and the United management team decided there was no option but to treat the problem with an injection.

As a result he looks set to miss England's forthcoming Euro 2008 qualifiers with Estonia and Russia later this month.

Speaking after the 1-0 win at Old Trafford, United manager Sir Alex Ferguson said: "Owen has had an injection in his knee and he'll be out for three to four weeks.

"This is an option we had from the very start, and if it resurfaced again we (decided we) would do that.

"So he's had an injection to try to clear the tendonitis in his knee."

Ferguson did, however, confirm that no operation would be necessary.

The news of Hargreaves' continuing injury problems was a rare negative on a generally productive night for the Red Devils.

The win, courtesy of Wayne Rooney's brilliant 70th-minute goal, his first of the season, puts United clear at the top of their pool, and well on the way to Ferguson's 10-point target which he believes will seal qualification for the last 16.

Their second straight win was far from a straightforward affair though, and Roma spurned a string of chances before and after Rooney struck.

But Ferguson refused to countenance the idea that his side had been fortunate this time around against a team they thumped 7-1 at Old Trafford in the second leg of last season's quarter-finals.

"I'm pleased with the result, it's a fair result, we controlled most of the match, carried a little bit of luck towards the end when they started to risk to play for an equaliser," he insisted.

"But I think in the main we deserved the result, in the first half we were too tactical and played with too much caution I think.

"The second half we improved and the goal was a fabulous goal - great movement, great passing, and the penetration we were looking for in the second half created the opening for Wayne, so it was an excellent goal."

Ferguson was, though, willing to admit to a certain amount of relief at the Italians' profligacy.

"I was relieved. I think it would have been unfair but then football can be unfair," he said of Roma's missed chances.

"I think we deserved that bit of luck because we played with good control, good football, good tactical awareness, so I was pleased with the performance."

He added: "Luck happens in football, no question about that. I think we got a break in the last 15 minutes of the match when they started to risk a bit."

The quality of Rooney's winner was particularly satisfying for the Scot.

After a burst of quick passing around the box, Nani prodded a deft through ball to the striker and he did not think twice about hitting it across Gianluca Curci on the run.

The shot rebounded into the net off the inside of the post and Ferguson was delighted to see Rooney finally get of the mark for the season following his spell on the sidelines with a broken metatarsal.

"It was only his fourth match and he is still trying to get his rhythm and real match fitness, that happens when you only play a few games," he said.

"But it will do him good, goals always do players good, particularly when goals are expected of them, so I'm pleased with that."

Cristiano Ronaldo was forced to leave the field before the end with a head wound and Ferguson confirmed the winger felt he had been elbowed by a Roma player.

The Portuguese needed four stitches to stem the flow of blood.

However it was Roma manager Luciano Spalletti who was left feeling bruised following a match he felt his side deserved to draw at the very least.

"Really this is a match where my players shouldn't be on the beaten side," he said.

"Even when you are playing against opponents of Manchester United's stature, with the players they have."