Smalling, 27, could have his role reduced at Old Trafford next season since the Red Devils signed Victor Lindelof from Benfica earlier in the summer.
He's already come under fire from Jose Mourinho last campaign as the Portuguese questioned his toughness.
And evidently he's worried he could see his playing time cut down ahead of next summer's World Cup, where he'll be hoping to be one of Gareth Southgate's first choice centre-backs.
The Daily Mail claim Smalling will now seek talks with Manchester United chiefs as he wants assurance he'll be a part of the first team plans next season.
There's likely to be enough games to go around at Old Trafford in 2017/18, with Mourinho's side playing in four competitions.
But the Mail add Smalling is likely to be relegated behind Eric Bailly and Lindelof in the pecking order.
United have also been linked with a move for Borussia Dortmund centre-back Marc Bartra which could spell further trouble for Smalling.
Although it's thought their primary transfer target going forward is Real Madrid striker Alvaro Morata.
