The Parkhead club continue their public and protracted search for a new boss following the departure of Gordon Strachan, who left three weeks ago after failing to win his fourth championship in succession.
McManus claims the Hoops squad are unconcerned about the Parkhead board's delay in finding their new man but insists that they are still coming to terms with losing their title.
He said: "It still hurts when you don't win the league.
"It hurts all through the summer.
"It doesn't go away and it's something that you need to live with and something that will drive you on in the next campaign.
"I know the lads will be feeling the exact same because I can assure you it hurts like mad when you don't win it.
"It is the quickest summer when you do win it and it's the longest when you don't, because you just want to get back and get things going again."
As a result of finishing runners-up to the Ibrox men, Celtic find themselves having to qualify for the Champions League group stages next season which means they will be back in action at the end of July.
McManus, however, is continuing is rehabilitation from a knee injury and will have to sit out Celtic's start to their 2009/10 campaign, as well as Scotland's World Cup qualifier against Norway in August.
He said: "I won't make pre-season. It will probably be the start of August before I start back training.
"I've not ruled myself out (of the Champions League games) because I could have a remarkable rehabilitation but the timescale now means I might be pushing it.
"I will give it my best shot but I have to make sure I don't do any damage in the long term.
"But I will be about the place and I will be working as hard as I can, the same as everyone else, to catch the new manager's eye and we will see how it goes."