The 21-year-old started for the Saddlers in their friendly against Villa on Tuesday and will be given another chance to impress against Ajax tonight.
After coming through the youth ranks at Liverpool, Brewitt joined Boro last summer in search of first team football.
But despite being made captain of their under-23s side, he was unable to break through and was told he doesn’t feature in Tony Pulis long-term plans at the end of last season.
And while Dean Keates has refused to confirm his identity, he did reveal the defender will be spending the next few days with the Saddlers on trial.
“Full credit to the lad he joined up with us at 6pm, just before the Villa game,” the boss said.
“It’s something that’s emerged and he acquitted himself well. He’ll be with us for the next few days.”
Keates also confirmed Walsall’s other trialist – a Cypriot winger – will feature tonight.
“He picked up minutes against Stoke and Villa and will get some more against Ajax,” the boss added.
“We will go from there, he’s done alright.”
Meanwhile, Keates confirmed Kory Roberts has undergone an operation after he suffered a double leg break in the friendly defeat to Stoke.
The 20-year-old, who was Walsall’s young player of the year last season, is now expected to miss the entire 2018/19 campaign.
“I went to see him (Roberts) on Saturday,” Keates said.
“He had his operation on Monday afternoon and it’s gone as well as it can.
“The lad has got a long journey ahead of him but we will gather round him and support him through it.”
Walsall have also confirmed promising winger Tobias Hayles-Docherty has joined Rushall Olympic on a trial that could lead to a loan move.
The winger has featured for the Pics in friendlies against Barwell and Walsall Wood.
“Tobias has gone to Rushall to get a bit of experience,” Keates added.
“It will help his development.
“It’s a trial to a loan, they just want to have a look at him.
“But all being well a deal will be in place before the season starts.”