He told BBC Three Counties Radio: "The gaffer called me, he told me to sit down, I thought I was getting dropped from the team completely.
"He said 'you're not going home because you're going out with the senior squad' and I'd take that over a day off."
Loach has benefited from former team-mate Ben Foster's withdrawal from Fabio Capello's squad for the friendly with Hungary on Wednesday, as well as Paul Robinson's retirement from international football.
The Ipswich academy product is not expecting to play a part in the match, but is not letting that dampen his spirits.
"It's where I've wanted to be all my life," he said.
"Even if it means sitting on the bench the whole game, just to have a training session and to be be named on that England programme is a big step for me.
I'm very proud that our small club can claim responsibility for a vein of England players over the last few years
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"If it's only the first step on the ladder I'll take that because hopefully there's much more to come."
Foster, 27, received his first England call-up while on loan at Vicarage Road from Manchester United and Mackay believes Loach's success is a reward for the Hornets' backroom staff.
He said: "To have a second goalkeeper at the club to go into the full England squad in the last three years speaks volumes for the youth setup, recruitment setup and Alec Chamberlain's coaching.
"I'm really pleased for Scott. I've known him since he was 17 years old.
"I think the amount of effort and time that he spends wanting to be a top goalkeeper, you sometimes get little rewards for.
"When that call came in from Ray Clemence to myself, I was delighted to be able to phone one of my players and tell him he's been called up for his country."
Loach has amassed 86 appearances for Watford since making his debut in a League Cup tie with Bristol Rovers in August 2008.
Source: BBC Sport
Source: BBC Sport