The Ulstermen were due to play Italian side Zebre in Parma on September 21 but the game was postponed and is now rescheduled for November 18.
But Muller believes everyone is ready to return to the playing field, adamant it is what Spence would have wanted.
"It has been an incredibly tough time, incredibly emotional, but Nevin would have wanted us to carry on and try to continue enjoying what we do," Muller said.
"The strength shown by Nevin's mum and sisters is inspiring.
"The Ulster squad has taken a huge amount of comfort from that.
"I believe everything in life happens for a reason and the faith and belief shown by the Spence family has been wonderful."
Ulster coach Mark Anscombe also added that getting back to action is the right thing to do.
"The lads feel comfortable around each other and they know they are among friends - it's easier for them to be together," Anscombe said.
"The support we have received from the rest of the rugby community is amazing.
"We respect everything that has happened but we have a job to do and we have to move on and perform well, as Nevin would have wanted.
"We must go to Cardiff and carry on with the job in hand."
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