Evra has been in excellent goalscoring form this term, finding the net four times, but his contract expires at the end of next season.
The 31-year-old has been linked with a one-year extension, but the report claims United have concerns over the Frenchman's defensive abilities, and are looking to draft in an understudy.
Alexander Buttner was signed for £4m from Vitesse Arnhem last summer, but has failed to make much of an impression. With Evra linked with moves to Paris St Germain, Monaco and Fiorentina, United are thought to be considering a number of left-back alternatives.
And Alex Sandro is one of the names under consideration. United sent scouts to watch the Brazilian in action against Malaga in Porto's recent Champions League match.
Sandro was brought to Portugal for £8m in a complicated deal involving Atletico Paranaense and Santos in 2011. The 22-year-old has six caps for his country
Everton star Leighton Baines is another in the frame, but the £15m valuation is believed to be a little steep for a 28-year-old.
Reports have claimed United will have their hands tied this summer by their expensive dealings in recent transfer windows.
Robin Van Persie and Wilfried Zaha represent pricey purchases, and United reportedly must first sell first-team stars to raise money for any substantial summer transfer activity.