He also used social media to call for others to join him in support for the cause and to "stand up for what we believe in."
Matondo, 19, has said that he did not know that McKennie would wear the armband prior to the day of the match but praised him for doing so.
"It was Weston's decision," Matondo said. "I spoke to him about it as well, on the matchday. I didn't realise he was doing it. If I knew I'd have got involved with him as well.
"It was his decision and he decided to do it himself and I feel like we need more people, if they believe that, to be strong enough to do what Weston's done. We saw other players do that at the weekend."
Floyd, who was black, died last week in Minneapolis after Derek Chauvin, a white police officer, kneeled on his neck for more than eight minutes. Chauvin, who was fired last Tuesday, was charged last Friday with third-degree murder and second-degree manslaughter.
Steffen, a goalkeeper at Fortuna Dusseldorf, issued a statement on Tuesday titled "Enough is enough" in which he said he was speaking in honor of "Floyd, Breonna Taylor, Ahmaud Arbery and every other African-American who has been killed by police brutality."
Adams, who plays for RB Leipzig, posted a picture of the boots he wore in Monday's game at Cologne, showing he had "Black Lives Matter" written on his left shoe and "Justice 4 George" on the right.
"As an African-American who day in and day out is proud to represent America in the worlds game, I'm saddened and frustrated," Adams wrote. "Collectively our voices will bring justice for these crimes. Enough is enough. Black lives Matter. Black lives inspire. Justice for Floyd. Forever one nation, one team. On and off the field."
On Sunday, Borussia Monchengladbach striker Marcus Thuram and Borussia Dortmund duo Jadon Sancho and Achraf Hakimi paid tribute to Floyd. Premier League clubs Liverpool, Chelsea and Newcastle have followed suit this week, posting messages of unity as they collectively took a knee during training sessions.
Paris Saint-Germain striker Kylian Mbappe tweeted out the hashtag #JusticeForGeorge on Saturday. U.S. women's national team stars Crystal Dunn and Alex Morgan voiced their support on Friday, with both players saying they were "sickened" by Floyd's death.
Laurens: Players should continue Floyd tributes like Sancho
Julien Laurens encourages players to continue to speak out about "Justice for George Floyd".
Meanwhile, FIFA urged football competition organisers on Monday to apply "common sense" and consider not sanctioning players demanding justice for George Floyd during matches after Germany's federation said it was considering a disciplinary case.
The laws of the game prohibit "any political, religious or personal slogans, statements or images" on equipment.
FIFA President Gianni Infantino stepped into the debate about Bundesliga players saying Tuesday that they should be applauded and not punished.
"For the avoidance of doubt," Infantino said, "in a FIFA competition the recent demonstrations of players in Bundesliga matches would deserve an applause and not a punishment."
European football's governing body will also overlook that rule to allow Floyd tributes in continental competitions it oversees.
"Football is a sport which encourages tolerance, inclusion and justice," UEFA President Aleksander Ceferin said. "These are the same values being espoused by those showing solidarity to George Floyd."
The Football Association in England endorsed FIFA's guidance and in a statement said: "Where any behaviours or gestures on the pitch that may constitute a breach of the laws of the game have to be assessed, they would be reviewed on a case by case basis with a common sense approach and understanding of their context.
"The power of football can break down barriers across communities and we remain deeply committed to removing all forms of discrimination from across the game we all love."
The Hungarian football federation issued a written reprimand on Monday to Tokmac Nguen for showing his undershirt with the words "Justice for George Floyd" in a match on Sunday.
Nguen, born in a refugee camp in Kenya to parents from South Sudan and raised in Norway, scored for Ferencvaros in its 1-1 draw with Puskas Akademia on Sunday.
The federation's disciplinary committee said in a ruling issued Monday that any similar actions by Nguen in the future would result in "actual penalties" on each occasion.
Schalke travel to face Union Berlin on Sunday, and Matondo said he is planning his own tribute.
"Right now, it's the perfect time [to send a message]," Matondo said. "I totally respect what the guys have done. Marcus Thuram, Jadon, Weston, Hakimi -- all the other players have got involved. I think it's amazing to show that courage and confidence to go out there and speak about what they believe.
"I feel strongly and respect the guys that went out and did it last weekend," he said. "I will participate in the best ways I can."
Matondo also said he feels that Floyd's death and the subsequent events in the U.S. have "really opened people's eyes" and hopes footballers will continue to make their own tributes.
"I feel like it doesn't matter what you're doing in sport, or if you're not doing any sport, if you feel like you should speak up in a certain way, yeah, then why not?" he added. "There's too much going on around the world right now, there's obviously destruction, a lot of things.
"So hopefully us footballers and the platform we have, I think it's perfect to speak up and say what you believe in."
The Associated Press contributed to this report.