The 33-year-old Messi, who scored a golazo but failed on a penalty kick in Paris on Wednesday, will be a free agent at the end of this season. Koeman made the case that Messi, who wanted to move last summer but was bound by an extraordinary transfer clause, may be more inclined to re-up with Barcelona because of its promising corps of young players.
"Leo's seen for a while that the team is improving with the changes we've made," Koeman said. "[There are] many youngsters with quality and a big future coming in, so it's not a question of having doubts about this team."
Besides the Dutch-raised Dest, who's been part of the U.S. national team program since age 15 when he played on Coach John Hackworth's U-17s, Barcelona's players 22 years old or younger Pedri, Francisco Trincao, Francisco Trincao, Oscar Mingueza, Ilaix Moriba. There's also Ansu Fati and Ronald Araujo.
"But only he [Messi] can decide his future," Koeman said. "No one can help him. He can see this team has a great future, so that's not an argument for him to [leave]."
Whatever Messi decides, Dest's Barcelona future looks much better than after the first leg's 4-1 loss to PSG when he was tormented by Kylian Mbappe in the Feb. 16 first-leg clash. But even then, Koeman seemed have Dest's back:
"Maybe because he has not been playing regularly and because he has had some injuries, that was an influence on his participation in the team," Koeman said. "But now he is OK, he's physically OK. He is  years old but he needs to learn, he needs to be more aggressive, he needs to be more concentrated. He had too many periods in the game where he's not 100% focused. We spoke to him about this."
On Wednesday, Dest hit the crossbar after a fast foray down the wing from his right back position in the 23rd minute in one of several impressive attacks. Last weekend, he started and went the full 90 in a 2-0 win at Osasuna and earlier in the week started in 3-0 Spanish Cup semifinal win over Sevilla. His first star after the 4-1 loss in Paris was in a 2-0 LaLiga win over Sevilla in which sparked numerous attacks. As was the case on Tuesday, he nearly scored but hit the woodwork.
In LaLiga, Barcelona sits in second place, six points behind Atletico Madrid with 12 games left. Even if Barcelona, now out of the Champions League, fails to catch up, Dest could win his first Barcelona trophy when it faces Atletico Bilbao in the Copa del Rey final April 17.