Foster joined United from Stoke City in 2005 for just £1million.
He said: “I want to be playing football, that’s the main thing for me.
“As a goalkeeper at my age now, that’s when I need to be kicking on — I need to get more games under my belt.
“The two years at Watford were fantastic for me to be able to play week in, week out and be number one.
“I’m not sure what the gaffer is thinking. If he wants to send me out on loan, it’s up to him, but I want to kick on here.”