The German arrived from Bayern Munich's second team in January on a short-term deal until the end of the season with a year's option but has so far made just one appearance as a substitute despite an ongoing injury crisis.
However, manager Tony Mowbray insists Haas is not yet ready for the physical nature of the npower Championship and will have to wait for his chance.
Mowbray said: "When I have seen him play against Cristiano Ronaldo for Bayern Munich against Real Madrid in pre-season, it seems strange to say but, in my opinion, at this moment he is not ready for the physical demands, the rigours, the intensity of the Championship.
"But if an opportunity comes and he grasps it with both hands and everybody says 'Why hasn't he been playing?' I'll sit here and say 'He hasn't been playing because he hasn't been ready but he is ready now and he's in'.
"He's got 11 games."
Source: PA
Source: PA