He was fit to figure in all four of Chile's games in South Africa, reporting back to the club last week.
"It's fantastic news that he's back and ready to play," West Brom boss Roberto di Matteo told the club's website.
"He's a quality player and I'm looking forward to seeing him progress in the Premier League."
We will assess his condition during the rest of the week before deciding what to do with him on Saturday Roberto di Matteo on Jara The game against Osasuna is the final chance for players to stake a claim to face Chelsea on the opening day of the Premier League season, and Jara may be a borderline case.
"Gonzo will be involved in some capacity on Saturday, I can't say at this stage for how long because this is his first week back at the club," noted Di Matteo.
"We will assess his condition during the rest of the week before deciding what to do with him on Saturday."
Striker Simon Cox will not feature against the team that finished 12th in La Liga last season - he has been unable to take part in full training because of an ankle problem.
James Morrison may be fit to play after recovering from a kick on the calf he received during the weekend draw at Coventry.