But fast-forward a few months and the English-born player, who qualified for Ireland through his grandparents and won 11 youth caps for the Republic, is far away from the Premier League and instead is rebuilding his career in Cyprus, lining out for Enosis Neon Paralimni, a side currently fourth in the Cypriot league.
"There's a lot of talk around the place about the game in Dublin tonight. They still talk about the 5-2 win over Ireland all the time, it was a famous win for Cyprus," Cassidy told the Evening Herald.
"Football is buzzing here in Cyprus, with the national team in good shape and a team in the Champions League but I still feel Ireland will be too strong for them. They are very confident ahead of the Ireland game, some people here feel that Cyprus can do it again and win in Ireland but I feel the Irish side will get the win.
"They are so passionate about the game here, everyone on the island is crazy about football. They are dying to pull off another shock against Ireland but I can't see it happening, the Irish side will have learned from past mistakes.
"I have seen a few of their players up close and when I came here on trial in the summer, the club had Demetris Christofi in their squad, he moved on to Omonia soon after but I got to see him, and he will probably play against Ireland tonight," added Cassidy, whose maternal grandparents were from Galway.
Cassidy was making steady progress at Bolton, playing regularly in the reserves and he was also on the bench for the first team on a number of occasions, including their Uefa Cup campaign, but he was never able to get a game for the first team, and the writing was on the wall when Gary Megson arrived as Wanderers manager.
"Since last Christmas, when Sammy Lee left Bolton, I fell out of favour at the club. Once Gary Megson came in I didn't even train with the first team any more, I didn't play in too many reserve games," he says.
"I still had six months left on my contract so I went in to see the manager and said that it wasn't working out for me. I didn't see myself progressing any further. The club agreed and let me go on trial to different clubs and that of course meant that the club didn't see a future for me there.
"I went on trial at Northampton, Doncaster, Luton and a few others. Doncaster offered me a contract and I was all set to take it but the youth team coach at Bolton, Peter Farrell, asked if I'd be interested in Cyprus. I spoke to an agent out here, I got a trial at Enosis Neon Paralimni.
"I had the trial and I was still planning on signing for Doncaster but I was surprised at the set-up here. The quality of the training and the facilities were good, I saw it as a club where I could progress, I liked the coach.
"I did well in the trial and they offered me a contract and I was happy to sign. I thought I had a chance to play first-team football, initially, and also to progress my career.
"The league here in Cyprus is getting better all the time, the club sides are doing well in the Uefa Cup and Champions League, so I hope to do well here, move on and maybe get back to a higher level at some stage.
"It was a challenge as no one had really done this before, coming out to Cyprus to play and get their career going."
So far, the move has suited Cassidy in some ways.
"The lifestyle is great, I have an apartment and a nice car, the beach is close and the weather and food are superb," he says.
"I am wary of getting side-tracked by the lifestyle. I am very close to Ayia Napa but I am not here in holiday mode, I am here to focus on the football and work hard.
"That's the key to me cracking it here, staying focused, because it can be hard, but I am adapting well.
"I am also learning the language. I was always good at languages, I speak German and I have picked up some Greek already, but I want to learn more.
"Football-wise, it has been a bit slow, I haven't played for the first team as much as I'd like.
"I haven't played in the league yet but we've only had four games, though I did play in a cup game and I did well. The coach here says I will get a chance, he has players he wants to give games to initially but, if I am patient, I will get my chance."
Cassidy was a regular in the Irish underage sides for a while, making his debut in an U-18 game against Malta in February 2006 and he went on to win 11 youth caps.
Now overage for the youths, he has his eyes on making it into the U-21 panel.
"I am hopeful that the U-21s can open up for me," he says.
"I always follow the Irish underage sides on the internet, I saw the U-21 squad for that game yesterday, a few of my friends were in it, like Jimmy Ryan, but I saw other players and I thought 'I can be as good as them'.
"It will take a while as I can't expect too much coverage of the Cypriot league in the Irish media but if my career can take off here, people might take note and I might get more caps for Ireland.
"I loved my time playing with Ireland and I learned a lot off the manager Seán McCaffrey. I hope to get a chance to play for my country again."