Speaking to reporters ahead of England's final warm-up friendly against Costa Rica, Tuchel was candid about the 24-year-old's condition.
"Declan (Rice) is on 100 per cent and Bukayo is still getting there, playing through discomfort at the end of the season, but obviously managing it and playing at a high level, but still not on his 100 per cent."
He continued: "Bukayo is just not there yet. Some things are missing, consecutive training. They took very good care of him and were very aware of it at Arsenal, and we will do a little bit the same."
Tuchel explained that Saka's late arrival to England's training camp was managed carefully and that progress has been steady.
"He was decisive in the second leg against Atletico Madrid to bring them to the final, he played the final. But like I said, he was managed in between, and this is what we do."
His assessment of what the tournament will look like for Saka was direct.
"I think it is very unlikely Bukayo starts and finishes all the matches from now on."
Saka first picked up the Achilles issue during the March international break, and missed out on those fixtures. He returned to play for Arsenal through the run-in — starting just five matches in the final phase of the season and completing 90 minutes only once — as the Gunners won the Premier League title and reached the Champions League final, where they lost to Paris Saint-Germain.
The Arsenal quartet of Saka, Declan Rice, Noni Madueke and Eberechi Eze were given extended recovery time following the Champions League final and joined the England squad late. Rice, Madueke and Eze are all at full fitness.
England open their World Cup campaign against Croatia on June 17.
Saka will be there. The question is how much of each game he will last.