Dalot was one of the Reds' better performers in the defeat at Newcastle United on Sunday – a game which Wan-Bissaka missed due to illness.
The latter could be back in the the squad for Wednesday's Premier League meeting with Brentford at Old Trafford (20:00 BST) after returning to team training.
But Ten Hag admits the pair's differing skillsets pose him a tricky selection puzzle, given both players have excelled during various periods of the season so far.
“I think it's really close, the competition between them,” Erik told reporters at his pre-match press conference.
“Maybe Aaron gives you a little bit more defending, Diogo gives you maybe a little more offence.