The 31-year-old scored eight goals in 18 games for Reading before returning to his parent club at the end of December.
He has seen been involved with Crystal Palace's first-team games since returning and eventually signed a new one-year deal today.
Clarke was a keen admirer on the forward and never gave up in his battle to bring him back to the club.
Speaking as recently as this morning, Clarke started to admit that it was looking unlikely.
"You never say never in football," he said. "But the deal for Glenn looks a lot more distant than a few weeks ago.
"If it’s not him then we’ve got other things we’re trying to make happen so if nothing happens it won’t be through a lack of trying."
Much has been made about Reading's shortage of strikers but Clarke let one go out on loan this morning.
Dominic Samuel has been in terrific form for the U21s this season and has five goals in his last two games.
He came off the bench at Huddersfield in the FA Cup but Clarke decided to let him leave to gain some valuable experience at Coventry City.
"He's a young striker we think about a lot," said the Reading boss. "He's very much in our thoughts and at this stage of the season it's good for him to go out, get competitive action and improve as a player."
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