Technical director Adam Braz said the left back was suspended on Wednesday by MLS while the league deals with soccer's world governing body FIFA and Cameroon's soccer federation to settle the dispute.
Oyongo was playing in the Africa Cup of Nations when he was acquired by Montreal on Jan. 27 in a trade with the New York Red Bulls.
His agent Nicolas Onisse and the Cameroon federation denounced the deal because the 23-year-old was not consulted before the move. The federation issued a statement saying Oyongo's contract was invalid because he was an amateur when he was loaned to the Red Bulls last season. It said Oyongo should be considered a free agent.
Braz said the contract is legit and he expects Oyongo to report, likely within the next two weeks.
"The league is pressing and moving forward with what they have to do, and we have all the documentation in place that shows clearly he's under contract with MLS," said Braz.
The Red Bulls announced Jan. 9 that they had purchased Oyongo's contract from his Cameroonian club, Rainbow FC Bamenda.
Less than three weeks later, New York sent Oyongo and midfielder Eric Alexander, a roster spot for a foreign player and allocation money to Montreal for midfielder Felipe Martins and the top pick in the allocation order, which they used to sign midfielder Sacha Kljestan from Anderlecht.
The allocation order is used to distribute U.S. national team players who wish to return to MLS from foreign leagues.
The risk in forcing Oyongo to report is that the Impact may end up with a disgruntled player. But Braz is confident he'll be happy in Montreal.
"We haven't alienated him," he said. "He's been given bad advice over there as to what his obligations are and whether he's under contract or not.
"We're clear and calm here. We know that once he comes here, he'll be welcomed and he'll fit into the group. He's going to enjoy playing here and he'll adapt to the culture really well."
Trading players is common in North American sports but is rare and often considered shocking in most of the soccer world.
But Braz said it won't stop him from dealing non-North Americans in future.
"We don't feel it's a precedent he's setting for others because he's wrong and, eventually, he'll have to report like any other player under contract," he said.
Oyongo, who played 13 games for New York last season, would probably step into the starting left back position in Montreal. He is said to be quick-footed and strong at both ends of the field.
The Impact ended the first phase of training camp Friday with a scrimmage against its under-18 academy players. Laurent Ciman, Jack McInerney, Ignacio Piatti and Dominic Oduro scored goals as the first team played the opening half. The team heads to Mexico for the next phase on Monday.
The club announced that it has waived central defender Karl Ouimette of Repentigny, Que., the first graduate of the team's academy to sign an MLS contract in 2012. Braz said Ouimette, who has seen national team action in recent years, would likely have had little playing time with a glut of defenders on the roster.