Despite appointing him as Erik ten Hag's replacement in November, the Red Devils' struggles have continued, and they currently sit 16th in the Premier League.
However, the former England captain has urged United to give Amorim time to implement his playing style.
“I think Ruben definitely needs to be backed in bringing in the players he wants but I actually don’t know how possible it is,” Beckham told The Athletic.
“I don’t speak to Jim Ratcliffe that often, only from time to time.
"Ruben needs to be backed as a manager to bring in his team and his philosophy; he’s trying that already but I think once he brings his team in and his players, then you’ll see something different.
"I’d like to think you wouldn’t have to sell your captain Fernandes. He has been exceptional. We’ve all been critical at times of some United players — but when we needed someone to step up, he has done it.”