Nothing screams deadweight more than an injury prone player who left the country for playing time only to return a few years later without succeeding in that.
Or when he was younger he believed he could make it as a starter, but now he's a little older he's more aware of his own limitations and is willing to accept a backup role at a big club instead of being a starter at a smaller one. He'd rather come here to play a minor role in league title challenges than a starring role in relegation battles, or even challenging for league titles in Greece or Turkey or whatever.
As a Celtic fan I've never understood why (besides money) so many players who would be fan favourites up here would rather be bit-part players in English teams but whatever, if Milik wants to be on rhythm guitar in Turin instead of lead at Panathinaikos that's fine with me. We've had plenty of cheap backup signings over the years, and actually I remember everybody freaking out over Giaccherini and Padoin as well because nobody considered they were coming as cover and were convinced every signing is an automatic starter.
Incidentally Milik is a cheaper deal than both of those I mentioned. We spent a total of about 7m Euro on Full Metal Giacch, and 5m on Padoin.
We can't have Vlahovic play every minute of every game. This guy will have a minor role to play and I think he'll be fine for it.