Mowbray, who lost David Wheater to Bolton in January, has since seen Matthew Bates and loan signing Andrew Davies succumb to hamstring injuries and, if Seb Hines fails to shake off a dead leg, will head into Tuesday's match against Nottingham Forest with just two fit central defenders.
That could mean a first Boro start for 25-year-old Haas, a January arrival from Bayern Munich's second team, following his appearance as a substitute against leaders QPR at the weekend.
Mowbray said: "If Seb doesn't make it, then we have got two fit centre-halves at the club [Haas and Jonathan Grounds] and they will both play.
"But I don' thin Max did anything that made you think, 'Oh, he's not ready yet'. He's fine.
"He's waiting for an opportunity. I will sleep on it on Monday and make the decision on who we think is going to do the best job against Nottingham Forest."
Source: PA
Source: PA