Sebastian Kehl says Shinji Kagawa would be welcomed back to Borussia Dortmund with open arms.
Douglas has described his arrival at Barcelona as the pinnacle of his career ahead of their visit to Villarreal on Sunday.
Morrison has not featured for the Blues since August and has been left out of the last three matchday squads with rumours Clark wanted to cut short his loan from West Ham due to concerns over the players' behaviour and attitude.
Those reports were denied by both Morrison and his agent - and Clark has now stated that with the Blues' next game not until October 20, all his players have an opportunity to force their way into his plans.
"Over the next couple of weeks everybody will be fighting for a place against Leicester," Clark told the Birmingham Mail.
"The lads that possibly haven't been involved have all got a chance to stake a claim and there are places up for grabs.
"But they've all got to be doing it on the training pitch first and foremost. Players get judged all time on how they train every day and how they go about their business."
Specifically on Morrison, he added: "I have had a good chat with Ravel this week and he knows where he wants to be and he knows how he's got to get there.
"We brought him in because he's a talented young man but there's more than talent that gets you in the team.
"Ravel understands that and he's going to be working extremely hard over the coming weeks to get that sorted."