Scottish champions Rangers signed Sweden Under-21 midfielder Mervan Celik on a free transfer on Friday.
Celik has joined All McCoist's side on a three-and-a-half-year contract after passing a medical.
The 21-year-old was a free agent after leaving Swedish club GAIS and becomes McCoist's first signing of the January transfer window.
"Mervan Celik has completed his move to Rangers after passing a medical and agreeing terms this afternoon," a statement on Rangers' website confirmed.
Celik had also been linked with English Championship (second-tier) clubs West Ham United and Middlesbrough.
He is yet to gain international clearance, meaning he will not be available to McCoist this weekend when Aberdeen visit Ibrox, but he should be free to face Hibernian next Saturday.
Meanwhile, McCoist insists he is unaware of a bid from West Ham for Croatian striker Nikica Jelavic and claims the reported figure of six million pounds (ê9.3m) would not meet Rangers' valuation.
"They have not made an official bid," he said. "The reported amount would not be enough to meet the demands of the owner. Six million is not nearly enough."