Salah scored twice to reach a half-century of Liverpool goals in midweek in a comfortable victory over Red Star Belgrade.
But he looked miserable afterwards – barely celebrating his strikes – and Merson thinks that is a clue to how he is feeling at Anfield.
And, with Real Madrid struggling and in desperate need of turning round their season, Merson thinks the move is on the cards.
“Mo Salah’s goals record for Liverpool is phenomenal but it’s only a matter of time until Real Madrid come calling,” Merson told the Daily Star.
“That’s some record, to be the fastest man to score 50 for Liverpool, especially when people are saying you are having a bad season!
“But if he keeps on scoring Madrid will come calling.
“How can they not? They need to do something big and they will want him in January. They are struggling like mad.
“If Salah wanted to go, Liverpool would be powerless to stop him.
“I can’t remember the last player to say ‘no’ to Real Madrid or Barcelona. It’s another level.
“Salah doesn’t look happy at Liverpool at the moment and we’ve seen this before.
“I watched him score against Huddersfield and his body language looked terrible. That would worry me if I was a Liverpool fan.
“If you take his goals away they’re not title contenders any more.
“Liverpool fans have seen big players leave before. They would be fuming if Salah left too.
“But this is what happens when you’re successful in the Premier League. The even bigger clubs come calling.”
Any move would see Salah become team-mates with Sergio Ramos, the man who left him sprawled on the pitch and who crushed his Champions League dreams.
But Merson said: “There was plenty of bad blood after last season’s final with what happened between Salah and Sergio Ramos. But would that stop him going there if they come in for him? No chance.
“Liverpool look like they could be around for a long time with the team they have now. So losing such a big part of if would be devastating for the fans.
“But I wouldn’t be shocked if Real Madrid make a big bid in January, and you know how these things work, there might already be some contact.”