Celtic are on a real rampage under Brendan Rodgers having gone unbeaten through the entire domestic season so far, winning 30 of their 31 games. It's a dominance that hasn't been seen in Scotland for generations and the Hoops look good on their quest for a potential treble of trophies.

In Europe too Rodgers' side progressed, reaching the group stages of the Champions League for the first time in three years. However, the groups themselves didn't go quite as hoped and although they had an incredibly tough pool, finishing bottom was not the aim.

One of the Celtic manager's big priorities this summer will be adding to his squad and building a team capable of being more competitive on the European scene.

Compared to most other teams in the Champions League, Celtic operate on a shoestring budget, so it's important to stretch their resources as a far as possible while also attracting genuine quality that can make a difference.

To that end, we're sure the club is scouring the continent for players they could sign on a pre-contract and land on a free transfer in the summer, as they did with Moussa Dembele last year. It's fair to say that gamble paid off, with the former Fulham man having been breathtakingly good in Glasgow.

Here are FIVE such out-of-contract stars that the Hoops should try to sign right now...

Callum Paterson

Football Soccer - Slovakia v Scotland - 2018 World Cup Qualifying European Zone - Group F - City Arena, Trnava, Slovakia - 11/10/16
Scotland's Callum Paterson in action with Slovakia's Robert Mak 
Reuters / Radovan Stoklasa
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A move for Callum Paterson of Hearts would add depth and competition to an area of the pitch that Celtic already have some top performers in. Mikael Lustig has been a key member of the Celtic squad for years now, always a solid option on the right-hand side of defence.

Paterson is a young player, just 22, who despite playing for Hearts has already won five international caps for Scotland. That shows the regard Gordan Strachan has for him and he'd know a bit about players who are ready to step up to European and international competition.

Currently out with a long-term injury, Paterson hasn't featured for Hearts since December so any prospective clubs may want to see how he comes back from that. Nevertheless, he is still an option for Celtic to pursue should they want to secure his services in the long-term. Signing up the most talent Scottish players is important to meet UEFA squad requirements and Paterson is one of those tipped for a bright future.

Joe Ledley

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Wales' Joe Ledley reacts
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A name familiar to all Celtic fans, Joe Ledley's contract at Crystal Palace is coming to an end and where better to make his next move than back to Glasgow? The Welsh midfielder loved his time in Scotland, striking up a real relationship with supporters and giving everything to make the Hoops a successful side under Neil Lennon.

At 30 he still has a lot to offer a top side and his performances for Wales over the last couple of years have shown he has the ability to mix it with some of the world's top midfielders.

It wouldn't be the first time Celtic signed him on a free if he does join, that's exactly how they landed him from Cardiff City in 2010 before he went to make over 150 appearances and score 30 goals for the Hoops.

Tosin Adarabioyo

Bayern Munich v Manchester City - Pre Season Friendly

Tosin Adarabioyo is a young Manchester City defender thought to have a bright future in the game. The 19-year-old actually made his only appearance of the season against Celtic at the Etihad in the Champions League.

He's at something of a contract stalemate with City according to The Telegraph, which is said to be causing some anxiety with staff at City who see him as a player with great potential. An England youth international at four age groups, it's clear he's well thought of by coaches down south.

Celtic are in a great position to land him compared to English clubs given they would have to pay minimal compensation for him, in a similar way to how they managed to bring Moussa Dembele in from Fulham.

The Hoops need to bolster their defensive ranks and doing so with a young up and coming defender could be the perfect scenario for both parties.

Mehmet Ekici

Mehmet Ekici has emerged as one of Turkish football's most effective and creative midfielders at Trabzonspor, coming to the end of a three-year spell at the club this summer.

This is a signing that would be a bit of coup with lots of sides with European ambitions probably looking at landing him on the cheap. Nevertheless with Champions League football as a carrot, who is to say that Celtic can't attract a player of his quality?

The Hoops need signings like these to push on in European competition and he would add serious playmaking ability to the Hoops' midfield, as he's able to play behind the striker or alongside the likes of Scott Brown and Stuart Armstrong.

Hasan Ali Kaldirim

Another star from Turkish football, Hasan Al Kaldirim is a name that was linked with a move to Celtic Park in January. A regular for Fenerbahce this season both in league and European action, he would provide significant competition for Kieran Tierney and perhaps serve as a replacement for the long-serving Emilio Izaguirre.

Brendan Rodgers needs depth in all areas and adding players with European experience is a massive bonus. He's an effective presence on the left flank both in defence and in attack, which we know the Celtic manager likes from his full-backs.

This is an area of the pitch that isn't a huge priority given the emergence of Tierney in recent years but if the Hoops can add quality and depth at a cut price then it seems like a no-brainer.