The 26-year-old US international visited Parkhead this week amid reports that Bhoys boss Brendan Rodgers is chasing his signature.
Nagbe was spotted at Celtic Park this week.
The reported Bhoys target was spotted at Celtic Park on Wednesday.
Former Rangers ace Kris Boyd thinks Darlington Nagbe would be a great signing for Celtic - but he wanted him at Ibrox in 2014.
Celtic target Darlington Nagbe was in the stands to watch tonight's game against Barcelona.
United States international Darlington Nagbe could join Celtic.
The defending MLS Cup champions will be looking to ride the momentum of last season's late surge into the new campaign.