The England international moved to Vicarage Road in the summer in the hope of kick-starting his flailing career after a tough time at Tottenham.
Yet his bright start in Hertfordshire was brought to an abrupt halt when Liverpool rocked up at Saturday lunchtime in a ruthless mood, with Salah the tormentor-in-chief.
Within the first five minutes, the Egypt international had hit the post and seen a shot blocked, before slicing open the defence with a gorgeous pass to find Sadio Mane to score his 100th Premier League goal.
After then forcing a fine save from Ben Foster and with Rose nowhere to be seen once again, Ashton questioned if there was something wrong with the 31-year-old.
"Rose is miles off it, absolutely miles off it," Ashton said live on air. "I don't think he's fit, I think he's got an issue, he's just not moving properly.
"Three or four times now Salah has simply accelerated past him, and he's got pace, Danny Rose."
He added: "I wonder whether Danny Rose has got an injury, he looks so off the pace it's unbelievable.
"He looks out of sorts, in a way that's more than just the bright start from Salah.
"I'm looking at his body language, he doesn't look right to me, he's not the Danny Rose I know and have seen so far this season.
"I would have taken him off after ten minutes."
Salah then got on the scoresheet himself with another simply stunning solo goal, as Liverpool took a 4-0 lead at Vicarage Road.
Twisting and turning through a packed Watford penalty area, the 29-year-old showed why some are hailing him as the most in-form player in world football with another draw-dropping strike.
And Ashton said it was even better than his wondergoal against title rivals Manchester City from before the international break.
"Mo Salah is not just the Egyptian King, he's the king of the world," said Ashton as he reacted live on air to yet another incredible Salah goal.
"It's a pleasure to be here to watch that. It's ridiculous, the footwork, the awareness of players…
"They think he's going to shoot but he drags the ball back, sits two defenders on their backsides and then slides it coolly into the corner. What. A. Player. What. A. Goal.
"We thought the one against Man City was out of this world… this is better!"
Four minutes after going down in his own box with an apparent injury, Rose was left to bemoan yet another Liverpool score as James Milner was given the simple task of finding Roberto Firmino in acres of space to tap in.
Boos rang around the ground at half-time, yet Watford just could not live with Salah and the rampant Reds.