NY Giants Owner Steve Tisch, 'Don't Count Eli Manning Out!'

Eli Manning still has the full support of NY Giants co-owner Steve Tisch ... who tells TMZ Sports, "Do not count Eli out!"

Of course, Eli struggled last year and was benched in Week 13 for Geno Smith. And, with the Giants going 1-2 in their first three games this season, some fans are wondering if the Manning era is over.

Not Tisch though ... who says he believes in the 37-year-old -- but wouldn't commit to Manning in 2019 and beyond.

"One game at a time," Tisch told us in Beverly Hills on Tuesday ... "We're going into Week 4. It's a long season. Hopefully an exciting season."

So, who would replace Eli if Tisch and the Giants have a change of heart? Technically, the #2 QB on the depth chart is Alex Tanney from Monmouth College.