Chelsea may be concentrating on their Champions League tie with Bayer Leverkusen tonight in their second last group stage match, but Andre Villas-Boas will have one eye on how his transfer targets perform as teams shore up qualification for the next stage of the tournament.

The Blues are on the lookout for upcoming stars to fill positions in both defence and attack in the January transfer window, and there is a group of players playing tonight that would suit the squad's new attacking style of play.

Hulk worked with Andre Villas-Boas before he left Porto for Chelsea in June, and the manager is still keeping watch of the star who has scored 40 goals in 80 appearances for the Portuguese side.

And as Porto take on Shakhtar Donetsk tonight, the 25-year-old will be out in force, and no doubt being studied by Chelsea scouts.

Neven Subotic and Thiago Alcantara are also long-standing targets for Chelsea, with the pair starring for Borussia Dortmund and Barcelona respectively.

And Kevin De Bruyne's coach at Genk said today that he beileved the youngster would fit in well into the Chelsea line-up, as a move in January to Stamford Bridge looks ever more likely.

And with that, IBTimes takes a look at five targets who Villas-Boas will be watching tonight.

The Hulk, as he's aptly named, has a massive bounty of €100 million over his head, but that hasn't stopped Chelsea from being connected to the Porto star after he played under Andre Villas-Boas at the Portuguese side. Hulk has said that he would consider a move to Chelsea if the timing were right, and with Nicolas Anelka on the out, Villas-Boas might be in the market for a new striker.

De Bruyne is one of Andre Villas-Boas' younger targets, and the 20 year old would be the Chelsea manager's fourth wonderkid purchase since he took over the managerial realm at Stamford Bridge. He stood up to the Blues when the sides played one another in the Champions League, and is said to be worth around £12 million, which would be a drop in the pond for Roman Abramovich.

Ballack isn't exactly a future target for Chelsea, but the side will be watching how their former star plays against them with particular care tonight. The midfielder made over 100 appearances for the Blues in 2006-2010, and although he wanted to stay at the club, Carlo Ancelotti didn't renew his contract and the midfielder went to Bayer Leverkusen on a free transfer. The Germany international coming up against his old side is an interesting twist of fate, and could make for a fiery encounter after Ballack starred against the club the first time around in the Champions League.

Subotic is fielding interest from both Manchester United and Chelsea, and just before the summer transfer window opened the centre back admitted that he sees his future in England. While Borussia Dortmund are in the Champions League, Subotic has said that he wants to play for a big club that can challenge both domestically and throughout Europe, and Chelsea would certainly fit that bill for the 22 year old. Having fellow Serbia international Branislav Ivanovic already at Stamford Bridge might persuade Subotic's final decision as well.

Chelsea are reportedly interested in both Thiago and his brother Rafinha, and while Thiago is in the senior squad, Andre Villas-Boas will no doubt have his eye on the 20 year old midfielder in preparation for the January transfer window. He has scored four goals in 24 appearances for Barcelona, and with tonight's match up set to be a fiery one with AC Milan, Alcantara's skills will be tested and shown off for clubs, including Chelsea, to judge.