Fletcher scored 37 goals in three seasons for Hibs before leaving for the Premier League earlier this week.
The Scotland striker's departure will put the onus on Derek Riordan, Colin Nish and Jonatan Johansson to provide the goals at Easter Road and Hughes has urged those players to show he does not need to sign a replacement.
Hughes told the club's official website: "I'm disappointed of course that I did not get to work with him, but Steven was in during the week and we wished him all the best. He was in to say
his goodbyes and you could see there was a tear in his eye.
"He had, I think, a good time at Hibernian, and you also have to acknowledge the work of those who brought him through, who coached him and helped in his development over the years.
"We'll miss him, so there is a gap there. Do I have to fill that gap or is someone who is already here going to say 'I'll take a bit of that'? We'll see. It's one thing talking about it. I've come across plenty of players who talk a great game but when they get out onto that pitch it's a different situation."