Heynckes, 72, came out of retirement to coach Bayern on an interim basis until the end of the current campaign, following the dismissal of Carlo Ancelotti in October.
Tuchel has been out of work since stepping down at Dortmund in the wake of their 2017 DFB Cup final win against Eintracht Frankfurt last May. The 44-year-old previously took Mainz into Europe for the first time in their history.
"Thomas Tuchel has the quality to coach Bayern." Heynckes told SPORT BILD on Wednesday. "He progressed through the youth teams at Mainz. That's the path to success that you must take, learning the right approach and people skills.
"Under Tuchel, Borussia Dortmund played excellent football with a good system - all the modern footballing elements that are prevalent today were plain to see. Tuchel's team finished runners-up, won the DFB Cup and played attractive football. I enjoyed watching BVB, that's why I respect and rate him as a very good coach. Dortmund aren't as good a footballing side now as they were under Tuchel."
The Bayern hierarchy had been keen on extending Heynckes' stay, but the former Germany striker, who has steered the Bavarians to the brink of a sixth successive Bundesliga title, into the UEFA Champions League last 16 and DFB Cup semi-finals, is committed to retiring in the summer.
"I took over because Bayern were in a difficult situation and weren't able to hire a coach they had faith in at such short notice," Heynckes said. "I said I would do it until the end of the season. That was the agreement, and I'm sticking to it. I'll be 73 in the summer and you never know how much time you have left. It was never my plan to coach again. There's more to life than work."
Watch: How Heynckes revitalised Bayern
Heynckes, who oversaw a Bundesliga, Champions League and DFB Cup treble in 2012/13, is enjoying his fourth stint at the Bayern helm.
Reports in Germany claim Bayern intend to name Heynckes' successor by the end of March.