The Hammers have seen great performances from James Tomkins and Winston Reid this season, but have been caught short in terms of depth.
After injuries to both Tomkins and Reid, Hammers boss Sam Allardyce has been forced to use James Collins and midfielder Cheikhou Kouyate in defence, meaning cover is needed this summer.
Onuoha, 28, came through the Manchester City academy before leaving for QPR in 2012, and the former England Under-21 international has played 91 games for the R's, including 18 this term.
Now a regular under new boss Chris Ramsey, Onuoha could be up for grabs this summer given that he has just over a year left on his contract - not to mention that QPR are edging closer to relegation to the Championship, which Onuoha may not be keen on.
It's believed that West Ham are interested, as are Premier League rivals Everton, Hull City and Stoke City - meaning the Hammers could face stern competition for the Nigerian-born defender if they do make a bid this summer.