However, only five of those appearances were starts, leaving De Boer interested in making a swoop as Palace look to bolster their squad before the transfer window closes.
"He is a very young, promising Scottish player of course," De Boer said ahead of Saturday's match away to Liverpool.
"He had a great year at Leipzig, though he didn't play in all the matches.
"He is from Great Britain, so it is always interesting to see those kinds of players and he is still very young. Maybe – but we are also focusing on other players.
"We want quality players who can improve the squad, are 100 per cent fit and can fit in directly with how we are playing. You are not going to throw money away."
De Boer will be without Wilfried Zaha against Liverpool due to a knee injury, a major blow after Palace lost their opener 3-0 to Huddersfield Town.
"Wilf Zaha is not fit," he said. "That is of course very negative news for us.
"Wilf's a very robust player, but we don't want to force it, because we need him for a whole year of course.
"It is still quite difficult to say how long it is going to take but I know Wilf is a player who wants to get fit again as soon as possible.
"He's a very important player for our team but we have to deal with it. Almost everybody [else] is fit but maybe not to play 90 minutes for example, Yohan Cabaye and James McArthur."