Yes. Handling 2 competitions is much easier than handling 3, especially when your teams have a small squad and have many injuries. When the league schedule release tomorrow, you will notice the time between league and CL matches can be as short as 3 hours. You may find difficult to arrange fit and well performing players to attend all matches. You may also not be able to make roster changes for the second matches.
BTW, as friendly reminder to newbies, the first league match is possible to start any time after new season day run. Get your team ready for the new season. Good luck.