Nate Burleson says the ex-running back definitely deserves consideration for it ... telling TMZ Sports, "Not first ballot, but should you consider him second ballot? Yeah."

Shaun rushed for 9,429 yards and 100 TDs in 119 career games for the Seahawks from 2000 to 2007. He also won the league MVP in 2005.

But, most NFL experts believe he's NOT a Hall of Famer ... saying he just didn't do enough for long enough to be among the league's all-time legends.

So, when we got Burleson -- who played with Shaun in Seattle in 2006 and 2007 -- we had to get his thoughts on Shaun's candidacy ... and he broke it all down for us.

"With Shaun Alexander, there's three tiers," Nate says. "Was he one of the best of his draft class? Yes. Was he one of the best of his era? Yes."

"And, can you write the story of football without him? That might be up for debate."

Nate says because of all that ... he believes HOF voters should definitely take a deeper look at Shaun when the next round of voting begins, telling us, "He should be considered."