Willett reached a career-high of ninth in the world after claiming his first major title at Augusta National in 2016, but has slumped to 442nd in the rankings after suffering numerous injuries and a loss of form.
A missed cut in last week's French Open was his ninth in 12 events this season, but the 30-year-old from Sheffield added a second round of 70 to his opening 68 at Ballyliffin to lie just a shot off the clubhouse lead held by Sweden's Joakim Lagergren.
Lee Westwood, who will be one of Bjorn's vice-captains in Paris in September, was a shot further back following a 71, while tournament host Rory McIlroy is six strokes off the pace after a disappointing 73.
"It's been tough to see somebody that good struggle for that amount of time but today was the Danny Willett of old and it's nice to see," Bjorn, who carded a 71 to finish level par, told Press Association, Sport.
"When you're in that situation the Ryder Cup and all those things are so far from your mind, you're working on a project that goes from day to day. Having two days like this is important, now comes the hard part of going out the next two days and enjoying it because you've done all the hard work to get back to here."
McIlroy, who won this title in 2016 but has missed the cut in four of the last five years, struggled on the greens for the second day in succession as he carded three birdies and four bogeys, three of which came in his last five holes.
"The game felt okay but I didn't hole anything again on the greens," McIlroy said. "I hit my best putt of the day on the 18th and it came back to me with a horseshoe. It sums up the last couple of days, even the good ones are not going in.
"It tested my patience and I was mumbling to myself walking from the 18th green to the first tee, but I will keep plugging away and at least I get to play the next two days. It's a success in terms of the last few years."
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