Motherwell have signed 21-year-old defender Mark O'Brien from Derby County on a five-month loan deal.
The Dubliner arrived at Fir Park after recovering from a recent ankle injury.
The Steelmen are short of defenders with Adam Cummins, Steven Hammell and Simon Ramsden currently recovering from injury.
And Zaine Francis-Angol may be added to that list after picking up a knock during the midweek defeat by Dundee United.
"I think Mark would probably have been with us if he hadn't gone over on his ankle in pre-season," explained McCall earlier this week.
"He has just been coming back to fitness now, so he's one we are waiting for.
"He started full training now so hopefully at the back end of the week, he will be a player we would like to get in on loan."
McCall has also brought Henrik Ojamaa back to Fir Park in a six-month loan from Legia Warsaw.