The Dutch international has scored one Premier League goal in 25 appearances since his arrival from Sporting Lisbon.
"I played Ricky because we had identified we could cause United some problems down the sides and in behind those centre backs," he said. "We felt Ricky gave us more movement than Gary Hooper, who got the goal against Liverpool. I don't feel we got enough of that.
"I wouldn't single one player out. We live and die as a team and we didn't cause them enough problems."