World number two Murray lost his second match of the clay court season in just 58 minutes as he made a total of 24 unforced errors and hit just seven winners. Read our report here.
Murray - the US Open champion - struggled from the off against Wawrinka and was unable to cope with his Swiss opponent's powerful groundstrokes.
His defeat was in sharp contrast to the preceding match on Court Central - Rafael Nadal's straight sets win over Philipp Kohlschreiber - and Croft told Sky Sports that the Spaniard's impressive display may have been part of the problem.
"I think we are all in a state of shock because Murray's match was over so quickly," said Croft.
"The first thing to say is that when Murray first went out on court everybody had left after watching Nadal, so there was quite a flat atmosphere; there weren't a lot of people in the stands.
"But Wawrinka got off to such a fast start. He had a very clear game plan - he looked so confident, so comfortable - and I think the biggest difference was that this match was the 12th that Wawrinka has played on clay this year whereas it was just Murray's second.
"There was a clear gulf in the comfort level out there. Normally you feel that Murray makes players feel so uncomfortable in his matches but this was quite the opposite - it was a real role reversal.
"The crowd, when they did come back from their lunch, were very, very appreciative of what they witnessed from Wawrinka and Murray did get a few boos, which I thought was pretty mean."
Following his defeat, Murray admitted that "it does take me time to feel comfortable on clay" and described the emphatic manner of his defeat as "disappointing".
Sky Sports expert Peter Fleming said that if Murray truly aspires to become the best player in world tennis then he must learn to adapt to his least favourite surface more quickly.
"It was a touch match-up for Murray on clay simply because Wawrinka is a powerful ground-stroker and, although Murray has become a more powerful hitter on a hard court, it's not really his favourite way of playing," said Fleming.
"On clay he reverts to a very consistent, conservative style because he's not quite certain what the bounce is going to be and when he does drop the ball short Wawrinka punishes it.
"It is a learning experience. The process of becoming the best player in the world means that you have to learn every time you step on the court.
"Usually, the matches you lose are the ones you learn the most from - they are the ones you can't gloss over by saying 'I've won, that's all that matters'."
Murray's former coach Miles Maclagan added: "To be honest, Murray didn't really show up.
"Kohlschreiber lost the previous match to Rafa Nadal 6-2, 6-4 and could possibly walk off court feeling ok about himself, but there will be a pretty horrible feeling in the Murray camp.
"As great as Murray is, there's no way in the world you can explain a one and two loss."
At present Murray is not scheduled to play in Barcelona next week so - unless he changes his plans - his next clay court appearance will be in Rome and then Madrid.
Croft has no doubt that Murray will not shirk the hard yards necessary on the practice courts to help him recover from this defeat and suggested that there were signs the Scot might be finding it tough to live up to his World No 2 ranking.
"He certainly looked extremely irritated when he left the court and I also thought it was quite significant that in the last game he didn't even wait for them to call time at the change of ends," she said.
"He'd already walked out onto the court - it was almost as if he was rushing to get that match over with.
"I think that is significant because as much as players will say they are trying to deflect what pressures are on them when it comes to world rankings by saying they are playing things match-by-match, every single time they go into a press conference and get asked about it, it does put that little bit of extra pressure on them.
"So perhaps Murray is feeling that a little bit this week. He'll certainly want to put that one behind him and if you have an early loss you've got a long time to wait until the next match on clay but I'm sure he'll be putting in a lot of time on the practise courts."