The England international striker collided with the Spanish goalkeeper during the first half of the sides' Premier League clash at Upton Park.
"Wednesday was beyond the pale," Ferguson told MUTV. "Let's be honest, there was an assault on him.
"But David de Gea stood up to it. He didn't let it affect him. He was brave and got on with his job."
United are currently at the top of the league table, while West Ham are 11th.