The Iron boss last night completed the signing of Ben Killip.
The former Norwich City youngster impressed in a recent match with Chelmsford City.
That means McDonald will have to be on top of his game to remain Braintree’s number one.
“Ben came in against Chelmsford and I thought he was superb,” said Quinton, whose side begin against FC Halifax Town on Saturday.
“He looks a very good goalkeeper and if he keeps the shirt then Nathan will have some hard work on his hands to get it back."
But fans won’t be seeing the new stopper for at least a week.
The manager added: “Nathan will miss the first couple of games as he got a two game suspension at Dartford.
“Someone threw a bottle on to the pitch and when Nathan threw it back off it caught the wind and got blown into the crowd.”