The manager accepted his team's lower ranking, Blues are 16th compared to Brighton's eighth, has denied them Lingard's services.
"I would love him back in a Birmingham City shirt but unfortunately lots of circumstances have meant that doesn't happen and we just have to move on," Clark conceded.
"The reason he is going to Brighton, who are at the top end of the Championship, is because they have seen how well he's done here.
"Initially when they [Man United] took him back they thought some Premier League clubs might come in for him on a loan basis in January. Whether that happened or not I don't know.
"Now they see Brighton at the top end of the Championship pushing for the play-offs - that's where they see his progression."
For breaking stories and all the great banter like us on Facebook: facebook.com/tribalfootball