Birmingham City have been granted clearance to finalise the signing of Senegal midfielder Papa Bouba Diop.
After being issued with a visa by the British Embassy in Paris, the 34-year-old former Fulham and West Ham man has been ratified by both the Football League and the Football Association.
He is now eligible for this Saturday's Championship home game against Leicester, but is unlikely to figure.
"The best-case scenario with Bouba is being on the bench," Clark told BBC WM.
"I had hoped it would be sorted over the weekend, and by Monday at the latest, and then get him back with us to play in a development game on Tuesday to assess where his match fitness was, like I did with Paul Robinson.
Birmingham City manager
“I can't afford to risk it with Bouba's match fitness. He's not played a competitive match since March”
"Paul's fitness levels were quite high up so he went straight in and he's proved that since he got in the team.
"But with Bouba, I couldn't afford to risk that. He's not played a competitive match since March. He got an injury at the end of last season for West Ham and wasn't in their starting line-up for the last 10 weeks."
Diop made his name in English football with Fulham after joining them from French side Lens in the summer of 2004.
He spent three seasons at Craven Cottage, playing alongside Clark in midfield,
before moving in 2008 to Portsmouth,
where he won the FA Cup in his first season with the club.
Having lifted the 2011 Greek Cup
during a year-long spell with AEK Athens,
he returned to England last season
with West Ham.
He played 16 times, rarely figuring after Christmas in the Hammers' promotion run-in, and was released in the summer, but has now signed an initial contract with Blues which will run until 17 November.
"I feel we need some sort of physical presence in the middle of the pitch," added Clark.
"I played alongside him for a while and we were partners in the centre of the pitch and I know what he's about.
"He's competitive because of his size and his physique, in the air and on the floor.
"He's obviously a threat in both boxes from set plays, but when he gets the ball down as well he can play."