The Austrian international joined the Hammers last season from Stoke City for a club record fee, and despite early struggles, did well towards the end of the season.
He scored 11 goals and provided six assists in the Premier League and played a pivotal role as West Ham escaped the relegation fears.
His good performance has caught the attention of Jose Mourinho, with reports from Manchester Evening News suggesting the Red Devils could weigh up a shock move for the player.
There is also interest from Everton in the former Werder Bremen star who earns around £100k-per-week at West Ham.
However, the Sunday People reports that the Hammers are not going to entertain any offers for the player, and they will dig in their heels with any club trying to lure him away from the London stadium.