There aren’t very many floor general type point guards in the NBA anymore. Most are scorers. Pass 1st guards coming out seem to be older players and get taken in the 2nd round.
Drafting a guy like that isn’t going to help the Celtics anytime soon and there aren’t many available via trade either.
So I looked at Euroleague guards that might have enough experience and skill to lead an NBA team, but the pickings are slim there too. A bunch of over 30 guys with experience that aren’t NBA athletes. Some NBA rejects like Shelvin Mack and Sergio Rodriguez. Yam Madar is probably as good an option as any.
Only one guy might be good enough to consider - Vasilije Micic - and if he’s the best Euroleague has to offer and hasn’t been signed by an NBA team already, then he probably isn’t worth signing either.
Did I miss anyone? Schröder and Rubio are better than anyone I found.