Care, who featured in four of England's RBS 6 Nations matches this year as they finished second, was overlooked when the 37-strong Lions squad was announced on Tuesday.
However the 26-year-old didn't let missing out affect his game as Harlequins defeated Northampton 22-19 in the final fixture of the regular season in the Premiership.
Care was at the heart of everything good about Harlequins in defence and attack as tries from Tom Williams, Rob Buchanan and Tom Casson proved enough against the Saints.
And O'Shea, who didn't have a single Harlequins player picked on the Lions tour party, is adamant Care could still feature Down Under this summer.
He said: "We certainly feel he [Care] should be there but, if he can keep fresh and maintain his form, history has often shown that players left at home get called up for Lions tours."