The Saddlers enjoyed a busy deadline day that saw them snap up Connor Ronan and Connor Johnson on loan from Wolves, while Mitch Candlin left to join Blackburn.
But they are still able to sign free agents – with Keates having held talks with one of his targets.
"There is still a possibility that we might be able to get someone in who has had their contract terminated," the boss revealed.
"I am hopeful for that one. And if we can do it, it will be a great addition to the squad and the football club."
Walsall faced an anxious wait to get EFL and FA clearance for the signings of Ronan and Johnson – with the paperwork submitted close to Friday's 5pm deadline.
But Keates revealed the deals were confirmed shortly before the Saddlers kicked off against Blackpool on Saturday.
Creative midfielder Ronan – who was on loan at Portsmouth last year – has been signed on a temporary basis until January.
Johnson meanwhile has agreed a season-long switch. And Keates is pleased to add them to his ranks.
"We got the okay for the deals just before kick-off on Saturday, it's all over the line," the boss continued.
"They are two good additions to the squad. Connor Ronan knows what the division is about and is a great little footballer. And formation wise he offers us something a bit different.
"And Connor Johnson comes in to provide competition at centre-half which is an area we have been a bit light.
"He gives us an extra body in there. Jon (Guthrie) and Jack (Fitzwater) have done 90 minutes since day one. He gives us a safety net."
Keates has stuck to a 4-4-2 formation in his time as Saddlers manager but he says the addition of Ronan gives him another option.
"He gives me options," the boss added.
"I watched him on numerous occasions last season for Wolves under-23s. "And then we came up against him when he played for Pompey.
"Watching their games leading up to ours, he is a good little footballer and he wants to play. He will give us something different."