But, on Tuesday evening, the duo will have to put their friendship aside when Enrique's Barcelona takes on an Ajax team managed by De Boer in the Camp Nou.
Hosting Barca go into the contest still smarting from their 3-2 defeat at the hands of Paris Saint-Germain on matchday two of the Champions League. It was their first loss of the season and also the first goals that they had conceded in all competitions this season.
With rivals Real Madrid to come at the weekend, there may be a temptation for Enrique to rest some of his key players, but reports have suggested that the Barca head coach has every intention of naming a strong starting lineup.
Meanwhile, visiting Ajax will have to make do without the services of winger Viktor Fischer, who is currently sidelined with a hamstring complaint. Aside from that, De Boer has no other pressing injury concerns.
The Dutch outfit have made 15 separate trips to Spain throughout their history and have five victories to show for their efforts. Their last win in the Iberian nation came at the expense of Atletico Madrid back in 1997.
Going into this contest, Barca are second in the group behind leaders PSG, while Ajax are a point and a place further back in third.
Possible starting lineups
Barcelona: Bravo; Alba, Mathieu, Mascherano, Alves; Busquets, Rakitic, Iniesta; Pedro, Neymar, Messi
Ajax: Cillessen; Van Rhijn, Moisander, Veltman, Boilesen; Klaassen, Viergever, Serero, Schone, Andersen; Sigthorsson
Sports Mole says: 2-0