Gleeson could be ruled out for up to three months with a broken foot sustained in training.
Chadwick suffered knee ligament damage, also in training, which could mean an eight-week spell on the sidelines for the midfielder.
Central defender Gary MacKenzie is closing in on a first-team return following a hip injury but is not likely to feature until January.
On-loan striker Patrick Bamford continues to have his hamstring injury assessed by parent club Chelsea, meaning Ryan Lowe will keep his place in the side.
Robinson's men were due to take on Doncaster on Saturday, but with the game postponed due to a waterlogged pitch, the Saddlers clash will be the promotion chasers' first game in 11 days.