Nolan and Carroll had chances to win the game for the Hammers and McDonald felt they proved there was no chance of split loyalties for the duo, as victories for Wigan and Aston Villa deepened Newcastle's relegation fears.
"They are 100 per cent behind West Ham," he said.
"Obviously they have a past with Newcastle and good times with them but they are so focused on West Ham trying to get in the top 10 now with two games left, after getting newly promoted and they've been solid all the way through.
"They've contributed as much as anyone in the team which is fantastic."
McDonald, who also spent time at St James's Park during his playing career, has backed the Magpies to retain their Premier League status.
"I've said before, I think Newcastle have got enough to stay up," he added.
"But everyone is slightly still under pressure with the result that Wigan have had so everyone needs to do the best in the next game to try and get the points on the board so they can't be caught, but personally I think they will be okay."