Janmaat was part of Van Gaal's Netherlands squad at the 2014 World Cup, when the Dutch secured a third-place finish.
He has the utmost respect for his former national coach, insisting he has nothing but praise for the Old Trafford boss and his side.
"I think they have a great team, with some fantastic players," Janmaat told the Shields Gazette.
"Also, the trainer is fantastic. He just needs a little bit of time. He is still fairly new there, and once he gets that time, I am sure he will win prizes for Manchester United.
"He is a fantastic trainer and he has had a magnificent career.
"I have been very fortunate to work with him, and I cannot say a bad word about him. He is one of the best trainers I have ever worked with, and if you see how he works tactically, it is great.
"He always seems to know what to do to win a game."
The two sides last met in December, when Papiss Cisse's penalty offered scant consolation in a 3-1 defeat for Newcastle.
