With Luke Shaw being sidelined with a broken leg for the next six months, can Saints exploit United's left flank going forward ?
With Shaw out United will either turn to Danny Blind who replaced Shaw after the injury at PSV Eindhoven earlier this week or Marus Rojo.
Although Blind would be the obvious choice in many ways in that he was the choice in the Champions League, Louis Van Gaal may feel that he does not want to lose him from the centre of defence.
If that is the case then he could turn to Marcus Rojo who was a possible signing that Saints looked at a year ago before turning to Toby Alderweireld.
This was perhaps a wise decision as Rojo has been less than convincing in his year at Old Trafford either in the centre of defence or at left back where he can also play.
This could be the key to Saints taking the game to United, Rojo's appearance as sub at PSV was his first outing of the season having been n unused sub in the other games, he will be not only ring rusty but playing in a side that is a little disjointed at the moment.
Whilst it cannot be denied that United have spent big and are a side packed with talent, they are not yet gelling as Swansea proved a few weeks back.
Their position in the League has been attained by two home wins against a misfiring Spurs & Liverpool along with a 1-0 win at Villa, so far the fixture list has been kind to them & they have yet to be tested in the Premier League by either a truly good side or one in form.
So so far no one is quite sure whether the big spending of this summer has improved the side after last season or whether like last, they will continue to be disjointed and a team of individual talent rather than a true team.
So Saints have the chance to attack them down their left flank and try to expose Rojo with the pace of Mane or even the guile of Tadic.
Clearly the toughest battle will be in the centre where Saints will have to tackle former Saint Schneiderlin and German legend Schweinsteiger, but if we can combat that threat and get the ball out to the flanks then we can use our pace to expose them, especially in their left back position where whoever plays there is not going to b used to the position and be comfortable.