Concerns were aired by Hartburn residents about animals getting stuck on land earmarked for 969 homes near Yarm Back Lane, Stockton.
But housing giant Taylor Wimpey says it is keeping an eye on the deer and they don’t appear to be distressed.
Worries about the animals being caught on fences were aired on social media – with hopes a means of escape could be provided.
Stockton South MP Matt Vickers criticised the decision to approve housing on the stretch.
He said: “I had hoped that they had at least taken all due care to ensure that wildlife and habitats were being safeguarded. The Labour-led council’s decision to concrete over our Greenfield sites is wrong for the local community and wrong for wildlife.
“I am alarmed at reports that deer are being left trapped and frightened on this land for such long periods of time.
“The council must work with the developers to find a solution to this problem immediately and establish appropriate gaps in the barriers to allow the deer to escape.”
Approval for the 969 home estate was granted by Stockton Council planning committee in a tight seven to six vote a year ago.
Traffic worries and some environmental impacts had been shared by objectors in the run up to the decision.
When it came to the wildlife, it’s understood an ecologist will have visited the site twice before the week is out.
A Taylor Wimpey spokesperson said: “We can confirm that a small number of deer have entered our development site in Stockton.
“The deer do not appear to be injured or distressed and are well away from any construction activity.
“Protecting local wildlife is a priority. Following advice from our ecological consultant we have created several openings in the site boundary to encourage the deer to leave of their own accord, and the site team has been fully briefed.
“We will continue to monitor the deer with our ecologist.”
Land off Yarm Back Lane had been earmarked for homes in Stockton’s Local Plan blueprint as part of a vast western urban extension set to bring more than 2,000 homes.
Stockton Council has been contacted for comment on the deer concerns.