After an injury to centre-back Winston Reid, McCartney was drafted in as a substitute for Saturday's game at Norwich and now hopes to be in a position to contend for a first-team spot.
The former Northern Ireland international has appeared just twice this season for the Hammers and is keen to put his injury-ravaged start to the term behind him.
"It was nice to be back on the bench but I want to get back to somewhere near where I know I can be and get in the team on merit rather than through injuries," he told West Ham's official website.
"There's a long way to go but I try and stay positive and I'm confident in my own ability.
"I've got to continue to be positive and believe I can get back on the pitch. It hasn't been easy at times, but I'm willing to work hard and hopefully I can get back to somewhere near the level I can play."
Now in the final year of his contract, McCartney is willing to play in any position in order to help out Sam Allardyce's side, who are currently four games without a win in the Premier League.
"Obviously I prefer playing at left back but there were a couple of times that I played games at centre-half," he added.
"If needs be and the manager has a few injuries then I can do a job there. Hopefully I can fight my way back in.
"It's going to be tough but we'll see what happens."