STUART ARMSTRONG trudged off the San Siro pitch in March with a sense of both injustice and belonging.

The negative emotions were triggered by the harsh reality that Celtic had just been knocked out of the Europa League by Inter Milan in controversial circumstances. An early red card shown to Virgil van Dikj was debatable in the least, and then an hour or so later a late goal from Freddy Guarin sealed the tie for the Italians.

But it was not all doom and gloom. Armstrong scored in the first-leg, a thrilling 3-3 draw, and over both matches this young Celtic side went toe-to-toe with European football royalty. It is the memory of doing well against serious opposition that makes the midfielder's appetite wet for the soon to start Champions League campaign. Why? Because that night in Milan proved to him Celtic belonged on that stage.

Inter Milan was a good experience. Barcelona, Real Madrid, Bayern Munich or Chelsea in the Champions League would be something else.

"That first leg was probably the most enjoyable game I have ever played in," said Armstrong. "Everything about it, the atmosphere, the noise, scoring was nice, too. It was also nice to get something out of the game. When John Guidetti made it 3-3 in injury time at Celtic Park, that made it most enjoyable and we felt we could get something at the San Siro. If there is more of them to follow, I can't wait.

"It's great to play in those games, but it's even better when you give a good account of yourselves when playing against a team such as Inter. To feel hard done by when you get knocked out, well that was a real vote of confidence.

"There were a few young boys in the team at the San Siro who had maybe not experienced that level of competition before. It was only my second time of playing at that level and it was encouraging to see the boys handling it so well."

The first qualifying match against FC Strarjan is now less than three weeks away and the Icelandic champions have been making positive noises, such as how they don't fear Celtic and that this tie is far from a foregone conclusion.

So this lot are not just about funny goal celebrations - do yourself a favour and look them up - and quite rightly fancy of pulling off an upset. Armstrong doesn't buy that but did warn against anyone, and some supporters have been guilty of this, thinking this will be a walkover, even if Celtic are well capable of coasting through both games.

"I would say they will be very tricky. A lot of people will be feeling we should get through, but it's a tough competition and all of the teams that are in it will be feeling they are there on merit, " said Armstrong. "It's going to be a challenging game. I've seen their celebrations. I'm impressed. The fish one is the best.

"They have their opinion about the game and they are entitled to it. That is irrelevant to us, we're focused on ourselves and our preparation. We won't be paying too much attention to anything. It is water off a duck's back. We'd like to make a good start and a nice win or putting ourselves into a nice position would be advantageous."

The fact Armstrong isn't a brand new boy at Celtic is testament to how much the club wanted to sign Gary Mackay-Steven and himself. They could have waited until now before signing both players and saved themselves a bit of money, but they were lured from Dundee United in January and neither have looked back.

Both scored on their debuts, at Partick Thistle, and then went onto contribute hugely to Celtic's title win. However, that would have happen even if the two had stayed at Tannadice for another five months, so despite their fine start, is this the true beginning of Armstrong and Mackay-Steven's Celtic careers?

"Yes, you could say that," agreed Armstrong, "It's good to make a little mark at the end of last season but now is the time that you really feel a Celtic player and you're starting again fresh for the new season and full of excitement.

"It's good that it didn't take long for us to bed in and that we didn't look out of place. I think we can take confidence from that and it certainly stands us in good stead for the season. To have that period just to meet the boys and get used to things and get used to the way of life here. Now we can come back in the summer and know everyone and not have to be the new guy and just focus on football."

And there is a lot of important football for Armstrong to focus on over the next weeks and months.