Houston, the Scotland assistant manager, described McDonald's officiating as "inconsistent" following last Sunday's last-gasp 2-1 defeat to Celtic, but he is yet to hear if his comments will be met with a punishment.
"I'm not going to comment on something I've not got yet," said Houston. "I'm not sitting waiting on the mail coming in."
Houston has more immediate matters on his mind, with Saturday's Clydesdale Bank Premier League meeting at Motherwell the first of two trips to Fir Park in four days.
The United boss is adamant his side are concentrating solely on the first encounter, rather than allowing their minds to drift ahead to Tuesday's Co-operative Insurance Cup quarter-final.
"I'll always think about one game at a time," said Houston.
"I won't even think about the cup game because it's an entirely different game. It's a different outlook - it's in or out and I'd rather get beaten 5-0 than go there and defend.
"It'll be hammer and tongs between the two clubs to try to get into a semi-final.
"But tomorrow (Saturday) is a different type of game where we can hopefully get in and about Motherwell, but we don't need to go kamikaze in a must-win game.
"We'll try to win every game and try to keep up our decent record away from home against clubs outwith the Old Firm."