It was Murray's first competitive game of rugby since helping the British & Irish Lions to a first series win in 16 years in the summer.
And although Penney had the luxury of calling upon Murray last season, the Munster head coach believes the 24-year-old has gone up a notch or two following his Lions success.
"Jeez, he looks fantastic doesn't he? How good is that kid?," Penney told the Irish Examiner.
"He can be the best in the world, if he's not already, he's not that far away. He's a bit of a genius.
"Coming off the back of having no football really, and having a 20-minute cameo like he did, superb.
"If you talk to him it [the Lions tour] was an eye opener for him but the kudos he got for running ahead of a couple of guys (Mike Phillips and Ben Youngs) with probably higher profiles and doing a great job on that tour against probably the best nine in the world, (Will) Genia.
"I think he did a sterling job with the way he played against him. And I think he knew I noticed how good he is and he ain't the finished product yet."