Brendan Rodgers has told Daizen Maeda to avoid an "it's not fair" mindset as he backed his return to top form for Celtic.
The Japan striker, who scored 33 goals last season, was denied a summer move because of the Hoops' failure to source an adequate replacement.
He was hooked at half-time in the Europa League game against Red Star Belgrade in Serbia on Wednesday night after struggling at centre-forward, with the Parkhead boss saying afterwards "he wasn't at his best, or anywhere near it".
It was Maeda's replacement, Kelechi Iheanacho, signed as a free agent the day after deadline day, who scored for Celtic in the 1-1 draw.
Ahead of the visit of Hibernian in the Scottish Premiership on Saturday, Rodgers said: "You can't underestimate how difficult it's been for him.
"This is a guy who has given absolutely everything for this football club and even sometimes when you want to give your best, there's a subconscious thing that can obviously hold you back a little bit.
"But, like I say to any player in this situation, it's so important that you don't get caught up in this sort of mentality of 'it's not fair', because when you get caught in that, it's very dangerous territory and it's hard to move on from.
"So you have to really look forward, really do it for your team-mates, do it for your family, do it for your supporters, and then eventually you get confidence back and you start to get back to your normal self.
"But he's been an incredible player for this club and I'm pretty sure over these coming weeks he'll get back to the form that he's shown.
"And I can only talk for my couple of years here. He's been absolutely sensational, so he will get back to that but it is always a challenge.
"It's not a light bulb you just flick on and off. This game's about emotions as well and it can be challenging for players.
"You're going to have dips as a player. If he was here and committed for four or five years, for example, you can still have dips in your form.
"And I think with Daizen it's very obvious just because of the level of work and intensity that he plays with.
"But I'm very confident that he will get back to the level and like I say he's a great person, he leaves everything out on the field.
"He's had this little issue around his ankle as well, which hasn't helped. But he will continue to give everything."
