Robbie Savage believes Manchester United will always have one over on Manchester City until the Blues win the Champions League.
City have managed just one semi-final appearance in the European Cup since Sheikh Mansour's 2008 takeover and Pep Guardiola is yet to take his side past the quarter-finals.
Monaco, Liverpool and Tottenham have eliminated City from the competition in Guardiola's three years at the club and Savage says it is a hurdle City must get over if they are to fully emerge from United's shadow.
"Pep Guardiola will never leave the neighbours over at Old Trafford completely in the shade until Manchester City win the Champions League," Savage said in his Mirror column.
"All the smart money will be on City to complete a domestic treble of title, League Cup and FA Cup against Watford at Wembley this weekend.
"But for all the glorious football they have played, and their astonishing stockpile of points over the last two seasons, they know the big prize Manchester United have already won three times has escaped them [the Champions League].
"United’s treble of title, FA Cup and European Cup in 1999 will remain the yardstick for greatness until it is matched – or even surpassed - by the Quadruple."
Savage added: "Is Pep grand master of the greatest team in the Premier League era when they have yet to win the Champions League?
"For me, that’s where United - who haven’t had much to shout about this season - can still lay claim to at least one crown.
"Until City win the biggest trophy of all, the European Cup, they will remain at least partly in United’s shadow."
