Tau, 27, scored for Albion in the previous friendly at Luton Town last Saturday but was not among the 23 players involved against Getafe tonight (Saturday, August 7).
The South Africa striker, who has made just one Premier League appearance for Brighton, has been heavily linked with a move to Egyptian top flight club Al-Ahly, where he would reunite with his former Mamelodi Sundowns coach Pitso Mosimane.
When asked why Tau did not feature, Potter said: "He was out for personal reasons. We will see how the weekend goes and go from there on Tuesday."
The Brighton boss also revealed that Ecuador midfielder Moises Caicedo missed out tonight due to a 'slight issue' with his knee after coming back from Copa América.
He added: "Hopefully it's nothing too serious but I didn't want to risk him for tonight."
Meanwhile, Potter did not confirm if Albion would be making more signings this summer but said the club is keeping an open mind.
"It's the boring answer but the truth," he said. "We have to keep looking until the window closes to see if there's anyone out there that can help the squad and the team.
"It's never straightforward with the window. I'm happy with what we have but always looking for ways we can improve."
Potter was impressed by Enock Mwepu, as he made his first appearance at the Amex since signing from Red Bull Salzburg
He said: "He's got that [energy] in abundance and brings that little bit something different.
"He can play numerous positions. It's about finding the best one got us given the game.
"He will give us versatility and some options. He'll get better and we'll get better."
Potter was also encouraged by the performance of Solly March, who featured at the Amex for the first time since February, after recovering from a serious knee injury.
"He's built up well over pre-season," he said. "He's stepped up minutes.
"He's in good shape and a good place. You can see his quality and he will get more game time."