Adrian Healey and LAFC coach Bob Bradley look back to 1998, when Bradley led expansion side Chicago Fire to MLS Cup glory. (3:05)

Los Angeles FC completed a deal to sign Mexico attacker Carlos Vela from Real Sociedad on Tuesday.

The Spanish club said a deal in principle had been agreed earlier for Vela to join the MLS expansion club in 2018, before the player posted a video of himself in an LAFC hat and jacket.

League sources confirmed to ESPN FC that the 28-year-old will become LAFC's first designated player when he arrives in January, as first reported by the Los Angeles Times.

Marca reported that the transfer fee would be about €5 million, after Sociedad paid €14m to bring him in from Arsenal in 2012.

Vela has played for Sociedad for the past six seasons, scoring 72 goals in all competitions, and will stay with Sociedad for the first half of the season in La Liga.

"I was fortunate enough to receive offers from many important clubs to leave this summer," Vela wrote on Twitter. "But because of my love and respect for Real Sociedad's colors, I'm committed to play for the next six months here and to bring my best every time I step on the field. My goal is to keep helping the team in every one of the competitions ahead.

"I arrived to Real Sociedad on August 16, 2011, as a player on loan and on July 17, 2012, I completed my permanent transfer knowing that I was coming to a great club. After that, I spent six unforgettable years in one of the best cities in the world."

Carlos Vela appears headed to MLS next season, reports say. Getty Images

The deal comes two weeks after the LA Galaxy, MLS's other team in Southern California, brought in Mexico's Jonathan dos Santos from Villarreal to join his brother Giovani.

LAFC, which hired former U.S. coach Bob Bradley as its first manager last month, has run into some difficulty attracting top stars as they prepare to begin play.

The club was recently rebuffed in its attempts to sign Dutch star Wesley Sneijder, who instead joined French club Nice on Monday.

And after sources told ESPN's John Sutcliffe in June that Andres Guardado, another Mexican midfielder, had agreed a four-year deal to join LAFC, he decided not to leave PSV Eindhoven and instead joined Real Betis in July.

LAFC has also been linked to an interest in Javier Hernadez, who joined West Ham; Wayne Rooney, who chose to return to Everton; and Zlatan Ibrahimovic, who appears to have a route back to Manchester United after he recovers from a serious injury.

A former Chivas youth product, Vela has spent his entire professional career in Europe since moving to Arsenal at 16 in 2005. After a series of loans, he joined Sociedad on loan in 2011 before completing a permanent transfer the following summer.

He has 17 goals in 55 international appearances for Mexico, though his relationship with the national team has been a contentious one since he was suspended for six months in 2010, then declined a call-up for the 2012 Olympics and again the following year for World Cup qualifiers.

But he has returned to the fold after rejoining El Tri after the World Cup in 2014. He scored against the U.S. in the 1-1 World Cup qualifying draw in June.