United consider Norwich's Aarons as a second option to fill their vacant right-back position if they cannot reach a deal with Palace for Wan-Bissaka.
According to Sky sources, United are preparing to make a second bid for Wan-Bissaka after having an initial offer of £40m rejected last week.
Talks are ongoing and United have indicated they will make an improved second offer - with Palace holding out for a fee close to £60m for the England U21 international, who has three years left to run on his current deal at Selhurst Park.
Sky Sports News understands Palace themselves hold an interest in Aarons, with Tottenham and Bundesliga side RB Leipzig also linked in recent months.
The Eagles are prepared to make a move for him if they do end up letting Wan-Bissaka leave for Old Trafford.
Aarons was named the EFL Young Player of the Season and included in the PFA Championship team of the year as part of Daniel Farke's title-winning side last season.
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