Former United captain Keane said: "I don't know where to start. I' m shocked and saddened about how bad they were.
"Everything about United, lacklustre, no quality, no desire, no characters. It's a long way back for United. It's scary how far they've fallen."
Ex-manager Mourinho also said: "We were bad last season and I don't see any improvement. I like these three (signings) they bring good quality but the team as a team I don't at all and I'm not surprised by the result and I don't think Ole can take any positives from the game."