The 22-year-old striker had loan spells at Hamilton and Morton under Gordon Strachan but had eventually forced his way in to Tony Mowbray's plans before the disastrous 4-0 defeat at St Mirren in March ended the Englishman's tenure.
McGowan was immediately dropped by interim boss Neil Lennon and resurfaced for the first time in the 2-1 friendly defeat against AZ Alkmaar at Parkhead on Wednesday night. He later revealed he had signed a two-year extension to his contract which was due to end in the summer but knows the challenge to find regular first time football remains.
McGowan said: "When the last manager (Mowbray) came in he said I wasn't part of his plans. Twice I could have gone out on loan but I knocked it back.
"I was confident I could push on and I kept doing well in training and the rewards came. Mowbray took a liking to me, played me and then his sacking came – but that's football. I thought I would have played more but it's not really been happening. So I need to do it all again.
"It's going to be hard but I'm up for the challenge. Neil knows what I can do and hopefully I can do it again.
"Neil phoned me up and asked me what was happening with my contract and I told him. He told me to come in to have a talk with John Park (Football Development Manager) and I was happy with the terms and happy to sign again.
"I was in a no-win situation. I'm not 23 yet. If I knocked it back then someone has to come in and pay x amount in compensation and to be realistic there is no money going around in the game. But that wasn't a problem, I was delighted to sign it and I am confident in myself, whichever manager comes in.
"I can't go in and say I want to play every week because it's Celtic and no player is guaranteed a game. But we will see where the new season takes me."
McGowan recalled returning to Celtic Park following the defeat at St Mirren to be met by jeering Hoops' fans, some of whom displayed a 'Mowbray Out' banner.
He said: "It's been a bad season all round, no doubt about it. Getting off the bus and seeing that... it was a terrible night, probably the worst night of my short career.
"But it's in the past now but it can only make me and the players stronger
"We need something, a lift to bring in the crowd and hopefully we can beat Rangers (next Tuesday).
"All the players know it's been a bad season but congratulations to Rangers, they have won the league. They have dug deep, they know how to win ugly and that's what we were missing. We were giving away soft goals but hopefully that can be sorted."
McGowan believes things may have turned out differently if Robbie Keane had been at Parkhead from the start of the season. The Irishman has scored 14 goals since arriving on loan from Tottenham in January and has impressed the Hoops' youngster.
"Robbie is a Premiership star and he has scored almost a goal a game," McGowan said of the Republic of Ireland international.
"It is great for me to train with players like that every day and I can only get better.
"His movement is incredible, he is a great professional and who knows, if he was here at the start of the season we could be sitting here with a different story."