It's been suggested De Gea will be sold this summer, with Dean Henderson to become the club's outright No1.
Thorstvedt told TV2: "Henderson has had to play quite a lot, especially now that de Gea has been away due to birth. He has played many cup matches and has done well. Therefore, many are wondering whether Ole Gunnar Solskjær will change goalkeeper.
"I doubt if it will happen. One must also take into account de Gea's status in the club. Releasing de Gea would be a kind of earthquake."
The Norwegian added: "It should be acceptable for Henderson to take one or two seasons where he plays something, but far less than half of the matches, and then in the long run show that he is a good competitor and take over."