Fernandes missed from the spot to squander the chance to salvage a point for United, who have now lost three of their past four games.
Ronaldo was also in the penalty area when referee Mike Dean pointed to the spot but Fernandes took responsibility for the kick. He blazed the opportunity over the bar, missing a penalty for United for just the second time in 23 attempts.
"That is football," Solskjaer said. "He will step forward every day of the week for the club and the team and sometimes it just doesn't go your way. It is such a fine line between heaven and hell."
Speaking after the final whistle, Solskjaer played down suggestions that Ronaldo had appeared unhappy with the decision to hand the ball to Fernandes.
"This is going to be the headline," Solskjaer said. "Bruno has been excellent and Cristiano is probably the one who has scored the most penalties in world football.
"It is just a missed opportunity to get a point. You will be making all these assumptions on the reactions of players. Bruno is such a good penalty taker and you would back him with your mortgage."
After back-to-back defeats, Solskjaer will be hoping to get back to winning ways when Villarreal visit Old Trafford on Wednesday. United are looking for their first win in the Champions League after losing their opening group game to Young Boys but the Norwegian is sweating on the fitness of Luke Shaw and Harry Maguire after both limped off with injuries against Villa.
"Sorry, I can't give you any updates," Solskjaer added. "We will have to get the scans done on Sunday or Monday."