Matthew Stafford better have brought his tough-guy helmet with him to Detroit this weekend ... 'cause Calvin Johnson tells TMZ Sports he's not expecting Lions fans to welcome their former QB with open arms.

Of course, Megatron says there will likely be some cheers and even some people decked out in Stafford's former No. 9 jerseys at Ford Field when the Rams visit for their much-anticipated Wild Card round game Sunday night ... but the Hall of Famer tells us, "I'm sure there will be people booing."

As for how Johnson will feel ... it seems he's feeling conflicted on how to handle it all as well.

"I'm definitely a Matthew fan -- that's my guy," said Johnson, who caught passes from Stafford from 2009 to 2015 with the Lions. "But I want him to come in here and come into the Lion's Den and not go home!"

Some Detroit fans, meanwhile, have already given a bit of a preview into how they'll respond when Stafford runs out onto the field later Sunday ... advocating a ban on wearing old No. 9 uniforms to the game -- something Matthew's wife was not pleased about.

Antics in the crowd aside, Johnson expects his old team will ultimately get the win over Stafford -- though he says the score will be very close.

Johnson also gave us an update on how the progress is going with his Primitiv Performance line ... saying he's hoping professional and collegiate athletes will be approved to use the new Primitiv products in the first quarter of this year.