Brendan Rodgers is on the verge of having the perfect Celtic season. He's won the Scottish League Cup, the Scottish Premiership and has also gone the entire league season unbeaten, the first time a Scottish team has achieved the feat in 118 years. Not only that but they are also aiming to win the Scottish Cup on Saturday against Aberdeen.

How do you improve on that?

Europe will be a start and the Celtic boss will be hoping to make progress on their showing in the UEFA Champions League this season after finishing bottom of their group.

In order to do that he'll need to have another strong summer transfer window and bring in first team stars of real quality who can enhance an already impressive squad.

Resources are at a premium for the Hoops so rather than inflate his squad further, the Celtic gaffer will likely also be looking to move out some players who don't have a future at the club.

Here are FOUR such stars, who have all featured for the first team at some point this season, who are unlikely to be hanging around after the summer...

Gary Mackay-Steven

Britain Football Soccer - Manchester City v Celtic - UEFA Champions League Group Stage - Group C - Etihad Stadium, Manchester, England - 6/12/16 Celtic's Gary Mackay-Steven looks dejected after a missed chance Reuters / Phil Noble Livepic EDITORIAL USE ONLY.

Gary Mackay-Steven made 10 appearances for Celtic over the season and none of them were especially convincing. Whereas former Dundee United teammate Stuart Armstrong has taken his chances and pushed on this season, Mackay-Steven has struggled to adapt and progress at the same rate as the rest of the squad.

Whether he heads out on loan or leaves the club entirely, he will hardly be missed in the first team which is a shame to say considering he seems like such a friendly and pleasant footballer.

The winger would be well suited to an ambitious Scottish Premiership side and with the likes of Aberdeen potentially losing Jonny Hayes and Niall McGinn, would a move to the Dons make sense?

Dorus De Vries

At one point in the season Dorus De Vries threatened to displace Craig Gordon as Celtic's number one under Brendan Rodgers. Signed last summer, he was predicted to offer a different kind of goalkeeper to the experienced Scotland international but in the end failed to hold down his place in the team.

After making just five starts, when Craig Gordon came on at half-time to replace him against Kilmarnock, he failed to start a game again for the entire season.

There may be an argument that says De Vries should stay at the club to offer back-up but at 36, he doesn't have many playing days ahead of him. Would it not make more sense to sign an up-and-coming goalkeeper that can really test Gordon and give Rodgers two quality options?

That's probably the ideal scenario with a view to potentially replacing the former Hearts man who, at the age of 34, is no spring chicken himself.

Nir Bitton

Nir Bitton has had more Celtic games than anyone on our list but ultimately hasn't shown enough to be considered a reliable midfielder in the side next season. Often lightweight and passive in the heart of the Hoops midfield, he's been usurped by the likes of Callum McGregor and Stuart Armstrong who have both offered far more defensively and in attacking sense than the Israeli international.

He does have sound passing ability and on his day can provide a calming, effective presence in the middle of the park, but those days are becoming rarer and rarer.

With the signing of Eboue Kouassi and the potential of another central midfielder joining the Hoops in the upcoming transfer window, we just can't see a place for him in the future of Brendan Rodgers' side.

With 38 appearances, 25 of which were starts, he's at least seen plenty of football this season. But in order for Celtic to truly hit the next level, he's one of the first team talents we'd consider replacing.

Saidy Janko

It's amazing to think now but Saidy Janko started five matches for Brendan Rodgers' Celtic at the start of the season, as one of the players to feature most during the UEFA Champions League qualifiers. However, he simply didn't show he had the quality to truly compete for a first team place at the club.

His performance in the Champions League play-off against Hapoel Be'er Sheva nearly cost Celtic the chance of making it to the group stages and he was quickly shipped off to Barsnley on loan for the season. He didn't have much success there either, making just 14 appearances, of which only 7 were starts.

If he can't get a game for Barnsley, we can't see him fitting into Celtic, especially with the likes of Mikael Lustig, Christian Gamboa and Anthony Ralston all showing good form this season.