The Baggies will then have the option to sign Gabr, who is an international colleague of fellow defender and close friend of Ahmed Hegazy, for a pre-determined fee in the summer.
Gabr, who has been assigned the number 16 shirt at The Hawthorns, and already plays with Hegazy at the heart of the defence for the Egypt national team, with both men set to go to the World Cup in Russia with their country.
"I'm here to help the team and do my job. I'm very happy and excited to be here," the 29-year-old, who has never previously played for a club outside Egypt, told WBA.couk.
Speaking about the deal, Baggies technical director Nick Hammond explained, "He's a player that we first identified at the African Cup of Nations where he played alongside Ahmed.
"We've continued to follow his progress since then and saw a good opportunity to do a deal in this window," he added.
"The structure is the same as for Ahmed - it's a well-structured deal for the club. Ali is strong, dominant in the air and he's got good pace as well. This is a great opportunity for him and we're delighted to have him here."
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