Portman will be on hand the day McCain is expected to name his VP.

(CNN) – Former Rep. Rob Portman — who reportedly figures high on John McCain’s VP shortlist — will attend the major campaign rally in Dayton, Ohio next week where the presumptive Republican nominee is expected to make his vice presidential announcement, amid mounting speculation the former Ohio congressman may join the GOP ticket.

Portman representative Rob Lehman confirmed that the former Bush official would be on hand at the event — which is scheduled for Friday, just hours after the Democratic convention officially ends — but added that his presence at the rally is not unusual. “He always tries to attend events when McCain is in Ohio," Lehman told CNN.

Portman campaigned on McCain’s behalf last week in Indiana.

Portman joined up with McCain unexpectedly Thursday.

(CNN) — Another day, another round of buzz surrounding a potential vice presidential candidate.

This time it's former Bush administration official and former Ohio Rep. Rob Portman, who made an unscheduled appearance aboard John McCain's Straight Talk Express Thursday afternoon. McCain and Portman are headed to Columbus, Ohio where the Arizona senator will participate in a town hall event with biking legend Lance Armstrong. (Portman will not be speaking at the event, CNN's Tasha Diakides reports.)

Portman, who served as Director of the Office of Management and Budget from 2006-07, has long been considered a top pick for VP. In addition to his economic credentials — something many political observers believe McCain's ticket desperately needs — Portman remains a popular figure in his home state of Ohio, the perennial presidential battleground that is once again expected to play a key role this cycle.

CNN's Political Market: Portman's VP stock on the rise

Portman represented Ohio's conservative 2nd district for 12 years, and could help shore up conservative support and working class voters there. Barack Obama lost to Hillary Clinton in Ohio by nearly 10 points in the Democratic primary — largely due to a lack of support from working class Democrats — though recent polls show the Illinois senator now holds a slight lead over McCain in the Buckeye State.

But it remains unclear just how high up on the VP list Portman is — Republicans may be wary of putting a former Bush administration official on the ticket, and he remains relatively unknown on the national scene.

And there's always the question of whether Portman is at all interested in the job. The former congressman appeared to suggest last month he was not.

Watch: Portman explain why he would say no to being VP

“Well, you know, I’m happy to be home,” he told CNN's Peter Hamby. “I commuted between Washington and Ohio where we are now for 15 years, and about nine months, so I made the decision to come home and it’s been great. I’ve got three teenagers, so I’m not looking for a way back to Washington right now."

“I love public service,” he added. “I want to help him. I think he’s the right person to lead the country at this critical time, but I’m not interested in going back to D.C. right now.”