Motherwell will have at least four teenagers in their starting line-up against Levante and more on the bench after being hit with a selection crisis for their Europa League play-off second leg.
Right-back Tom Hateley and midfielder Nicky Law both have knocks and are not travelling to Spain. Shaun Hutchinson is suspended following his red card in the 2-0 first-leg defeat and his fellow centre-back Simon Ramsden has not recovered from a hamstring strain.
"We're without Steven Saunders long term, Hutchinson, Hateley, Ramsden, so we ain't got that many options in defence," McCall told Press Association Sport. "It's our eighth game in a month and we've got a few players missing. We'll have to put out a young side."
Forward Michael Higdon is also an injury doubt while Omar Daley is facing a bureaucratic challenge to make the game.
While the rest of the Motherwell squad were checking in at Glasgow Airport on Wednesday morning, the Jamaica international was in Edinburgh at the Spanish consulate trying to secure a visa.
There was some good news after Chris Humphrey shook off an injury that forced him off in a reserve game against Hearts on Monday.
"He got a knock and came off in the bounce game we had, but he is fit to travel," McCall said. "Higgy is coming with us and we'll assess him over there. But there is no Law so that's four first-team regulars not travelling."
Motherwell ended their 1-1 draw with St Mirren on Sunday with five teenagers on the pitch - defenders Zaine Francis-Angol, Fraser Kerr and Adam Cummins and midfielders Steven Hetherington and Stuart Carswell.
"I would imagine at least four 19-year-olds will start," McCall said. "We've added Lee Erwin, Josh Watt, Euan Murray and Adam Ashgar to the squad and they are travelling with us. At least three of them will be on the bench.
"So it's going to be a very youthful team."