By FOX Sports Staff
O'Shea, who played over 250 games for United, watched as his Sunderland team slumped to a 1-0 defeat on Saturday which kept Sir Alex Ferguson's men on course for a Premier League-FA Cup double.
The Sunderland defender left United in July 2011, but not before winning five Premier League titles with the Red Devils. He dismisses the notion that this season's United team are not as good as past squads including the famed 1999 treble winning side.
"The manager [Ferguson] has been fortunate. He's had some great squads to select from but there's no doubt this squad are up there with the best of them," O'Shea said in the Daily Mail.
"They've got a tough game against Chelsea away from home [in an FA Cup quarter-final replay on Monday] but they're more than capable with the squad they've got.
"They were able to leave players behind and still come away from here with a win. The manager has got pretty much everyone fit and they'll go from strength to strength."
United had looked on course for the semi-finals of the FA Cup when they jumped out to an early two-goal lead at Old Trafford against Chelsea through Javier Hernandez and Wayne Rooney.
However, Rafa Benitez's side replied through strikes from Eden Hazard and Ramires before United keeper David de Gea was forced to pull out a terrific stop on Juan Mata to set up Monday's replay.
"They [Chelsea] really deserved to win the game in the second half, although we could have been four-up in the first 20 minutes," Ferguson was quoted on ManUtd.com as saying.
"De Gea's save was one thing, but I also thought we were scrambling about to get through the game. But we're fresher now and we've got a strong squad in terms of picking two teams."
United will face Manchester City in semi-finals of the FA Cup should they navigate their way past Chelsesa.