McCartney, who suffered knee ligament damage in training, has not featured for Sam Allardyce's men since December 9 but made a welcome return to the matchday squad for Sunday's 2-0 defeat at Chelsea.
"It has been a long time out and the last time I played 90 minutes was December," he told West Ham TV. "I had a run out on Friday night for the Development Squad and it was good to play the full game on Tuesday and get a positive result.
"The knee's feeling good, I think I probably need a bit more fitness and a bit more sharpness but that will come with the next few days' training and hopefully some more game time.
"I've only been back training for about ten days to two weeks. The next game's not until the end of March so that gives me a bit of time to do some more training, more fitness work and I'll be raring to go come the West Brom game.
"To be honest I was bit surprised to be on the bench against Chelsea on Sunday, it was nice to get away with the squad again and hopefully come the West Brom game I can maybe be pushing to get back in the team, if not try to play some minutes as a substitute. But it's nice to be part of the team again and over the injury that I had."