The two Corkonians put in encouragining displays at different ends of the field last night against Dinamo Bucharest, with 23-year-old Miller forcing Angelo Alistar into conceding the decisive goal in their Champions League third qualifying round first leg clash.
Keane, who slotted in beside Mikhael Silvestre in the United central defence, said: "We saw against Dinamo what he is capable of. He gets into dangerous situations and we have seen with Celtic what a danger he can be."
"I think he can do really well for United because not many people really know about Liam and there's no big pressure on him. So, please God, I think he can be very good for us."
United manager Sir Alex Ferguson, who must contemplate his side for Sunday's Barclays Premiership opener against Chelsea without nine squad members, added: "Liam showed great assurance and confidence and did really well. He was a bonus for us."
Keane, 32, who was named last week alongside Miller and Waterford-born John O'Shea, another United star who played out of position in midfield last night, in Brian Kerr's squad for Wednesday's friendly against Bulgaria, also commented on his defensive jaunt.
"The boss wanted to play me there because of my pace... no, I think he wanted my experience at the back," claimed Keane, "we didn't want any mishaps and we did a good job in the end.
"A couple of years ago we lost 1-0 in Hungary at the same stage and didn't want to take any chances. There was some pressure when we were 1-0 down but we knew we could get an away goal and hopefully when we get back from Old Trafford we will have one or two back from injury."