In addition to Nigerian international Peter Odemwingie serving the second of his three-game suspension, Baggies boss Steve Clarke also has a long list of injury doubts including Steven Reid and James Morrison, who are both struggling with hamstring injuries.
Downing is concerned the lack of reinforcements could harm his side's chances of overcoming the competition holders Liverpool at the Hawthorns, and admits some of the club's younger players could deputise.
|LEAGUE CUP LATEST
|22/1||Liverpool are 22/1 with Bet365 to beat West Brom 3-0 on Wednesday
“We’ve got nine players out at the moment, including Peter Odemwingie,” Downing told the club's official website.
“That’s obviously going to have some effect on our selection. We’re hopeful one or two who are 50/50 for tomorrow will come through.
"James Morrison came off with a hamstring strain on Saturday, so he is doubtful. Steven Reid and Goran Popov are among the nine players as well. We’ll check on one or two players tomorrow.
"But if there is an element of doubt over any player I think they won’t play.”
Downing has also hinted that summer signings Markus Rosenberg and Yassine Al Ghanassy could get their first taste of first-team action since joining the club, but admits they need time to adapt.
“With Yassine it’s just about acclimatising to the British game," he added. "He has that ability with the ball but he just needs to learn about the other side of the game.
“Although he’ll be chomping at the bit to play it’s important he takes these two or three months just to learn about the game.
“Markus is one who brings international experience and he’s another one we’re optimistic about. Hopefully, he’ll get some part of it tomorrow.
“George Thorne, Scott Allan and Saido Berahino, and James Hurst, who has a little knock, are all likely to be involved in the squad."