The 25-year-old Portuguese spent Tuesday undergoing a medical in Berkshire after a fee that could rise by a further £2m was agreed between the two clubs.
Wednesday are keen to off-load a couple of strikers before Thursdsay’s 5pm deadline with caretaker manager Lee Bullen admitting last week that six on the books is too many.
Jordan Rhodes is expected to attract interest with Norwich City having already had a cheeky offer to take the striker on a free transfer knocked back.
The Canaries could return for someone who spent last season on loan at Carrow Road, while The Yorkshire Post understands another couple of clubs are monitoring the situation with a view to making a late move.
Joao is expected to be officially unveiled at the Madejski Stadium on Wednesday.
Signed by Wednesday for £3m from Nacional in 2015, the Portugal international has netted 28 times in 126 appearances. The last of those came on Saturday – ironically against Reading – as the Owls started the campaign with a 3-1 victory.
Despite having an abundance of talent, Joao has never fulfilled his potential at Hillsborough and had a spell on loan at Blackburn Rovers in 2016-17.
Wednesday, meanwhile, expect to hear in the next 24 hours whether their Carabao Cup first round tie against Bury will go ahead next week.
The Shakers are due in S6 next Tuesday but their first two League One fixtures have been postponed amid a financial crisis at Gigg Lane.
Bosses at the Football League took the step of suspending the opening day clash with Milton Keynes Dons and Saturday’s trip to Accrington Stanley after Bury failed to show the governing body evidence of its financial viability.
The Lancashire club, promoted to League One last May, have already been given a 12-point deduction for the season after entering into a company voluntary arrangement (CVA) in order to try to clear some of their debts.
Wednesday have moved to sign experienced goalkeeper Paul Jones in the wake of Keiren Westwood’s red card on the opening day.
With Joe Wildsmith ruled out for up to three months, Cameron Dawson would have been the only senior goalkeeper at the club going into Saturday’s derby clash with Barnsley.
“This is a huge football club and I am really pleased to sign,” said Jones, who at the age of 33 has more than 350 appearances to his name.
“I have come in as number three with Joe picking up an injury in pre-season and I know there’s a huge amount of hard work ahead.
“Things can change very quickly in football. We have seen that with Westy’s red card at the weekend and Joe’s injury so you have to be fit, sharp and focused and ready to step up.”
Across the Steel City, Ched Evans has left on a permanent deal to Fleetwood Town. The 30-year-old has signed a two-year deal after Sheffield United agreed an undisclosed fee with the League One outfit. Fleetwood have the option to extend the stay of Evans by an additional year.