After testing all possibilities, the best attitude is: don't say anything! Several players will be disappointed because they were expecting some congratulations, but this will not change their performance. Obviously, don't forget the congratulations at the end of the match.
I did it with a team in Ivory Coast. There is a delay. I was champion of Ivory Coast in June 2015 and started the matches for the ACL in Spring 2016 (for the final stages in Fall 2016).
even more 'realistic': after finishing 8th (!) in French Ligue 1 and winning the France' cup, i was contacted by Chelsea and Man Untd (no, i did not have Martial in my team).