Scott Forrester (Luke Kleintank) had an important reason for leaving FBI: International After season 3. In the first three seasons of the police procedural, Forrester was the head of the elite Fly Team, which investigates international crimes that threaten the security of the United States or violate the rights of US citizens living abroad. Like most shows in the One Chicago universe, Forrester had his fair share of cast turnover, though he was a regular until the end of season 3.
The team's adjustment to new leader Wes Mitchell will be a powerful arc FBI: International Season 4. In the season premiere, Mitchell arrived in Budapest and asked for Fly Team's help to catch an international criminal who killed his LAPD partner, but Vo convinced him to become their permanent leader after the case was solved. While Vo knows and trusts Mitchell, others on the team may not. However, Forrester's absence this season isn't just for story purposes Luke Kleintank chose not to renew his contract At the end of season 3.

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Luke Kleintank left the FBI to spend more time with his family
Kleintank's decision demanded that the FBI: International must explain Forrester's absence
Kleintank announced his departure FBI: International shortly after the series' 4th season renewal. He said he would like to spend more time with his family, although he is grateful for the three years he spent on set Deadline). This decision meant that the series had to find a quick way to write her character, as she was only a few episodes away from her departure.
Kleintank was the second actor to leave
FBI: International
In season 3, as Heidi Reed left at the beginning of the season.
The last episode of Forrester aired on May 7, with two new episodes left in the season. Thus, Forrester is reported missing in action. Meanwhile, Chicago Med alum Colin Donnell joined the cast as an NSA agent who temporarily leads the team in his absence. By the finale, it was revealed that Forrester was hiding in Russia with his fugitive mother, ending the possibility of him returning to Flight Team after being found.
How Wes Mitchell Connects with Scott Forrester at FBI: International
The new Team Leader doesn't know Forrester, but he does know Vo
There is no direct connection between newcomer Wes Mitchell (Jesse Lee Soffer) and Scott Forrester. Mitchell is an LAPD cop who comes to the rescue of the Budapest Flight Squad. After his partner was shot, Mitchell tracked the killer down to Budapest, which led him to the Flight Squad. It was a surprising introduction, as it was widely assumed that the FBI would find someone to be the permanent leader rather than leave it up to chance to find the right person to fill the position.
While Forrester was level-headed and tried to resolve conflicts with local law enforcement diplomatically, Mitchell had already demonstrated that he was more impulsive and willing to take risks in the pursuit of justice.
Mitchell's presentation was made easier by having worked with Vo before. Mitchell was once his trainer and therefore trusts him. Vo also promoted Mitchell to become their permanent leader, which led to Soffer replacing Kleintack. FBI: International may go more smoothly than expected. It also helps that it has a completely different personality than Forrester. While Forrester was level-headed and tried to resolve conflicts with local law enforcement diplomatically, Mitchell had already demonstrated that he was more impulsive and willing to take risks in the pursuit of justice.
Could Scott Forrester still be returning to FBI: International?
His Exit Was Open Ended, But It Would Be Difficult
Forrester wasn't killed, so technically he can still return to Flight Team. However, he is now a fugitive because he helped his mother escape to Alaska. It would be difficult for him to return to the Flight Team because he would have to be arrested and removed from the FBI for helping his mother escape when he was wanted by the FBI.
If only Forrester had returned FBI: International, This could be in a dramatic story where the Flight Team is required to track down and arrest their former leader, leading to divided loyalties and compelling conflict. However, this story will end with him either facing justice or evading recapture, and it is unlikely that he will ever return as leader. Regardless of Forrester's return to the series, Mitchell will remain the leader of the team.
Source: Deadline