Wolfsburg coach Felix Magath is considering all disciplinary options against Diego after the Brazilian stormed out of a team meeting.
Diego left the team's hotel after learning he would only be on the bench for Saturday's crunch game with Hoffenheim and did not make contact with any Wolfsburg officials until reporting for training on Sunday.
Magath said his behaviour was not only unacceptable, but may also warrant legal action.
"I have never known anybody to leave the team meeting before," said Magath.
"We will have to see what legal implications it may have - that is up to our solicitors.
"We will have to ensure that we solve the problem correctly with the help of UEFA and FIFA. Anything is possible."
It appears as though Diego, who joined the Wolves last summer for over 15 million euros, has played his last game for a club who only avoided relegation to the second division with victory in his absence on Saturday.
Germany legend Franz Beckenbauer has already had his say on the matter, telling Sky television: "I find it disrespectful to leave the team in such a situation.
"That is not on; it is a sign of a bad character.
"I cannot imagine Diego having any kind of future under Magath."
Despite the distraction of Diego's antics, there was nevertheless joy and relief for the 2009 champions with their 3-1 win sealing their Bundesliga status.
"We are delighted and relieved," said Magath "It was an incredibly stressful 90 minutes.
"We started well, but then we eased off and only when we fell behind and were practically in the second division did the team show a different face.
"I was certainly tense and I have never experienced a finale like it."