I highly doubt he was forced to play. He probably could sue if he was forced to play, and since I haven't heard anything of the sort, and the fact that after the match he came out and said that he was desperate to play, I don't think any force was necessary. Hargreaves himself's doesn't say anything of being forced to play as well. Just says he was selected for the match by Ferguson. He could easily say "No Guvnor, I don't want to aggravate my injury anymore." And he'd be well within his right to do so.
Why shouldn't he publicly raise concerns? If he raised concerns with the doctors and physio's and they didn't listen, surely raising them publicly would of helped matters. Maybe made the a few enemies within United, but I think that would of been better then spending 3 years injured, since according to him, he probably would of gotten better treatment, got better and then may have helped United win a few more trophies which would of helped the recent enemies become friends again.
Also it is an attack on United. Basically saying that United's medical team ruined 3 years of his career, and its disrespectful. United have tried to help him for 3 years, paying his wages, medical costs and everything, all for him to say that he received the wrong treatment and its United's fault? Even worse considering he said it while at Man City. Could of said it while he was a free agent, but no. Decided to say it while at a Rival club, just to rub it in.
He's a great player, But after these comments, he's a bit of a ****.