Bristol chairman Chris Booy has demanded an improvement in displays, saying the club have "massively underachieved".
Booy told BBC Radio Bristol: "As a club we have underachieved massively.
"[That was] one of the reasons why we wanted to get Andy Robinson involved."
Middleton was sacked following a review by Robinson, but Booy played down rumours that the pair were unable to work together at the side, who currently lie fifth in the Championship table with 17 points after 18 games.
"We hoped Andy and Liam could work together but results were going against us," Booy continued.
"We decided to make an earlier decision so that Liam could go and look for something else to do and now Andy will be more involved in coaching the side.
"I don't think it's about them working together - this is a results-based business but Andy has had a month to assess where we are going and the view is he needs to get more involved in the day-to-day coaching of the side to take us forward," Booy added.
However Booy praised Middleton for his efforts during his time at the club and with the academy, adding: "Liam is a honest and decent man and tried his hardest to work and do the best he could."