Valdes was forced to train on his own following an alleged fall-out with van Gaal but he insists there is no ill-feeling towards the man he describes as a father figure.
The 34-year-old told Sky Sports News HQ: "I feel like a professional footballer again after all those hard days in Manchester.
"It's difficult to explain, but it was hard being alone. Sometimes at United I thought 'I don't need this', but I am a fighter and a professional."
"He's like a father figure to me. I don't want to remember the last six months in a bad way - for me he is in the top. We are still friends and there is no problem between us.
"I want to say in a public way thank you to the U21 coach Alan Fettis - without him I may have given up football. He made me keep going and stopped me when I was thinking about bringing my career to an end."