As a player himself who always shows heart and commitment, the Pompey defender appreciated everything he saw about the thrilling 3-1 win on Wednesday night.
That result sent United through on away goals after losing the first leg 2-0, representing a remarkable turnaround.
It was crowned with Rashford delivering the killer blow to the French side in the 94th minute.
That victory provided so much drama it earned comparisons with many great late shows from previous Manchester United teams, including the 1999 Champions League winners.
Clarke enjoyed the match and he praised the England forward who showed nerves of steel.
Being faced with that sort of pressure to net a late penalty to win such a big game is not a position the Pompey defender would be too keen on.
He said: ‘I watched the match and you have got to admire Rashford’s bottle in a moment like that.
‘To have so much pressure on young shoulders. You have really got to take your hat off.
‘It’s not a situation I’d want to be in. So yes hats off to him and in my opinion it was definitely a penalty.
‘He stepped up. That can almost make or break a player.
‘I suppose if he crumbles and skies it or does something like that it could be detrimental to his career.
‘So it showed what a top player he is and what great bottle he has.’
Since taking over as manager until the end of the season, Ole Gunnar Solskjaer has masterminded a spectacular run of form for United.
It’s a huge contrast to when Jose Mourinho was in charge.
But Clarke doesn’t feel it always can be put down to the individual in charge.
He added: ‘I’d love to know how much Solskjaer is really doing around the place because sometimes it can just be a change and things sort of take care of themselves.
‘They are on a good run. They are doing well.’
With four Premier League teams still in the competition, it could well be time for English winners of Europe’s biggest competition again.
Spurs and Manchester United have reached the last eight, while Manchester City and Liverpool will be hoping to join them.
City face Schalke on Tuesday with a 3-2 lead and Liverpool go to Bayern Munich on Wednesday after a 0-0 first leg at Anfield.
Clarke would like to see the trophy lifted by an English side and certainly wouldn’t be counting Manchester United out after their Paris wonder show.
He added: ‘With so many good teams it is a lottery really. If they (Manchester United) get a favourable draw I don’t see why they can’t go deep. I’d like to see one of the English clubs win it. It is always nice.
‘With the four teams still in we’ve got a few chances and hopefully one of them steps up.’