Troubled Man Utd still world's biggest club says Coventry boss Robins
Robins began his playing career with United and famously scored the FA Cup third round winner against Nottingham Forest in 1990 that is often credited as saving Alex Ferguson from the sack.
United's current manager Erik ten Hag is also battling to hold onto his job after a difficult second season for the Dutchman.
Ten Hag's side are almost certain to miss out on a place in next season's Champions League.
And United, who last won the Premier League in Ferguson's final season in charge in 2013, are winless in four league games since reaching the semi-finals with a victory over Liverpool.
Losing to second tier Coventry would be a huge blow to Ten Hag's hopes of persuading United's new co-owner Jim Ratcliffe to keep faith with him next season.
But Robins, who left United in 1992 to join Norwich, believes his old club's problems have been overstated.
"People, pundits, are talking in a derisory way about Manchester United and what they're doing, how they're performing," Robins told reporters on Friday.
"For people who are talking about Manchester United are this or that, or they concede lots of shots: you're talking about a team that is full of talented players, top international players.
"We know they are clearly favourites to win this game, by a million miles, simple as that.
"They can hurt anybody on their day. The game against Liverpool their goals were outstanding. So you've got a lot of things to consider, especially as a Championship club going up against the biggest club in the world."
Coventry, who won the FA Cup for the only time in 1987, reached the semi-finals with a dramatic 3-2 win over Wolves thanks to stoppage-time strikes from Ellis Simms and Haji Wright.
Robins' side, currently eighth in the second tier, were beaten by Luton in last season's Championship play-off final and he hopes that experience of Wembley will help his players pull off a massive upset.
"We've already given the fans a special occasion getting there. Being in the national stadium with Manchester United, it doesn't get much bigger than that," he said.
"It's a brilliant opportunity for everyone and there's a lot of excitement around the city. There is a global reach there for Coventry City, the world will be tuning in and it's a great occasion for all of our players."