Pierre-Emerick Aubameyang has been left out of Chelsea's Champions League squad.
The 33-year-old started all six group matches, scoring two goals - but has not started a game since 6 November.
New signings Enzo Fernandez, Mykhailo Mudryk and Joao Felix are all included.
"Pierre's a professional and I understand he will be disappointed. It was a tough decision," said Potter.
"We had three coming in and two had to go out. He was the one that has missed out. It's absolutely nothing bad against him. He has done nothing wrong at all."
Aubameyang was left out of their squad for Friday's 0-0 Premier League draw with Fulham, with 20-year-old January signing David Datro Fofana coming on in the second half.
"We wanted to give David some game time today to see where he is at," said Potter. "Pierre's just unfortunate and he will be fighting for his place for the rest of the season.
"He has handled it very well and trained today fantastically which is what I'd expect. He's been a top, top guy for us."
France defender Benoit Badiashile, a £35m January signing, also misses out of the Champions League squad.
England Under-21s winger Noni Madueke, a recent £30.7m acquisition from PSV Eindhoven and fellow new arrivals Andrey Santos and Fofana were also excluded.
Chelsea travel to German club Borussia Dortmund in the first leg of their last-16 tie on Wednesday, 15 February.