The Dane, who was announced by the Bees on deadline day, sealed a six-month deal with the west London club as his eagerly-anticipated return to football was confirmed.
Eriksen has not played competitively since he suffered a cardiac arrest in Denmark's Euro 2020 opener against Finland.
And Frank admits it is a 'miracle' that the Dane is healthy enough to make a return to the Premier League.
"It is a little bit of a miracle of course that first and foremost he is healthy but also that he wants and feels ready to play football again," Frank said.
"I would say no (concerns). Of course, I am not a doctor but all the specialists who have seen him, met him and tested him know that everything is perfect. I know Christian and his family would never take the slightest risk in that sense that something could happen when he is training or playing a football match.
"For me it is down to the mental part of it and getting back into rhythm, playing football at a top, top level and managing it, which I expect will be fine."
"Christian will arrive on Sunday and train with the team on Monday. That will be his first training session," Frank said.
"Of course I have been speaking to him a lot the last few weeks, more since December, but he has a physical coach and they had Zoom meeting with our head of performance this week to make sure we hand over everything in the best way.
"Christian has a solid physical foundation and has been doing all sorts of tests. He has been running a lot, training a lot, so he has done quite a lot over the last few months so his foundation is fine, but another thing is to get up to match speed.
"It is hard to say when he is available. I will know a lot more after Monday."
Quizzed on whether it could be months before Eriksen debuts for Brentford, Frank admitted: "I hope weeks, a few weeks, but I don't know. I am much more clever when I have seen him train."
Frank labelled Eriksen as potentially Brentford's 'greatest signing' and conceded his return to the pitch - seven months after he suffered a cardiac arrest in June - will be an emotional moment.
"We got it over the line and that was fantastic," the Bees boss, who tested positive for Covid-19 on Sunday and is currently self-isolating, added.
"It is potentially the greatest signing ever for the club. I spoke to a fan last night and he mentioned a guy about 70 years ago who was at potentially the same level.
"But the story behind it, I think it will be an unbelievable day the day Christian steps on the pitch. You guys have seen him performing as one of the best in the Premier League and what happened to him in June was crazy and a shock for us. The day he returns it will be emotional."