Colin Kaepernick is continuing to work on his case against his former employer, the National Football League. In a report by Yahoo Sports, NFL columnist Charles Robinson reports that sources say that the former San Francisco 49ers quarterback's legal team will seek federal subpoenas for not only President Donald Trump but also Vice President Mike Pence and any other political office that has knowledge of the president's stance on NFL player protests [VIDEO].

Getting a subpoena to the president will be difficult

Kaepernick's legal team will make the case for a presidential subpoena on the basis that Trump has had talks with multiple NFL team owners about player protests, including those who kneel during the national anthem.

Kaepernick would want to use these conversations to make his case against the league, and to get Trump to give his testimony.

Being that this case that Kaepernick started has included only the NFL and its owners, getting a subpoena and testimony to and from an outside political source will be difficult under the league's collective bargaining agreement. Colin Kaepernick's lawyers will have to make a detailed argument stating that the words of the president are vital in order to be granted a subpoena.

Why subpoenaing Donald Trump matters in Kaepernick's case

Kaepernick was released from the 49ers in 2017, the offseason after he started a movement that has taken America's culture by storm. Today, most of the NFL and its players have taken part in some sort of protest. Trump made it known [VIDEO] that he was not on the side of the players on this one.

He has stated before that players should be fired for such protest.

According to The Hill, Kaepernick's grievance states that "Trump and Pence engaged in various public relations stunts designed to retaliate against Mr. Kaepernick's peaceful protest.'"

The grievance also calls Trump "'an organizing force in the collusion among team owners in their conduct towards Kaepernick."

Recently the NFL chose its stance on player protests. The league chose to come out with a new policy to take effect in 2018 that states that all player and team personnel must stand on the field during the performance of the national anthem. Otherwise, those who choose not to must stay in the locker room.

President Donald Trump also chose to cancel his invitation given to the Philadelphia Eagles to celebrate their Super Bowl victory at the White House.