Most clubs and leagues around Europe are gearing up for the second half of the domestic season now following a winter break with managers glad to have had the time to help players recuperate from injuries and knocks. The opening of the transfer window also gives them a moment to assess whether reinforcements are required to cover for those facing extended spells on the sidelines.
Injuries occur at every club of course, and the modern-day squad is built to withstand such instances, though a month or two without a star player could certainly hinder a club's title aspirations, or chances of surviving relegation for that matter.
Two such key players who have been missing recently are Real Madrid's Marcelo and John Terry of Chelsea, both of whom are on the way back to full fitness.
Update on key Manchester-based duo:
Manchester City face a massive test of their ability to retain the Premier League title on Sunday with a trip to the Emirates Stadium to face Arsenal, but they will do so without star striker Sergio Aguero.
The Argentine forward tore a hamstring muscle against Stoke City and though he is hopeful of making a swift return, it is unlikely he will be fit in time to face the Gunners (per Guardian).
Aguero, who scored the title-deciding goal in the last minute of last season, has hit eight Premier League and two Champions League goals this season, making him City's joint-top scorer along with Edin Dzeko.
After the Arsenal match Aguero will have a further week to recover before his team's next fixture—but then Manchester City face three matches in 10 days and Roberto Mancini will be desperate to get him back on the pitch before games against Fulham and QPR as well as an FA Cup Fourth Round tie.
Over the other half of Manchester, United are facing an equally important match at home to fierce rivals Liverpool—and they are likely to also be missing one of their key forwards.
The former Everton attacker has scored eight goals in all competitions this season, seven of them in the Premier League, though has played much of this season in an advanced midfield role instead of as an out-and-out centre forward.
Rooney's likely absence will be tempered by the presence of top scorer Robin van Persie, who has already scored 20 goals for United since his move from Arsenal last summer.
Real Madrid's left-back has been missing in action since mid-October when he broke a bone in his foot training with the Brazil national team. The national team doctor immediately said the defender would be absent for three months (as per Guardian), and that appears almost nailed on to the day, with Marcelo finally making his return to his club's first-team scene now.
Manager Jose Mourinho has used a series of players in his place on the left side of defence, with Fabio Coentrao unable to hold down a spot because of poor form and his own injuries.
Now Real have received a big boost with the news that Marcelo is about to return to first-team action, and could be included in the squad for the Copa del Rey clash against Celta Vigo (via Goal.com).
With his team struggling back in third place, 16 points off leaders Barcelona, Marcelo will be a welcome addition to the match-day squad for Real who will hope that an increasingly-settled back line will be the catalyst for improvement over the second part of the season.
Chelsea captain John Terry has missed his club's last 15 matches having been out since November with a knee injury sustained against Liverpool.
It was initially suggested that the Blues' captain would be out for around three weeks (via Guardian), but it has proven a more difficult injury to overcome than first thought. Terry missed the Club World Cup in December because of the injury, and has yet to play for new manager Rafael Benitez.
Terry is still some way off a return to action for the first-team but may begin his comeback in an under-21 match this week, according to his manager (as per Daily Mail). Chelsea have the joint-best defensive record in the Premier League so have not exactly been unable to cope without him, but they will still welcome him back to bring cover to their defence.
With David Luiz pushed into midfield recently, Chelsea have relied on the partnership of Branislav Ivanovic and Gary Cahill in central defence.
Terry has made just six league starts this season for his team.
Premier League: Returns for Key Players
Elsewhere in the Premiership in England, several players are set to return to action for their teams after time on the physio's table.
Liverpool hope to have Fabio Borini back in training soon, while Newcastle have badly missed Yohan Cabaye. Both players should be back available in the next week or two.
Norwich City striker Grant Holt, Fulham goalkeeper Mark Schwarzer, and Arsenal's injury-plagued central midfielder Abou Diaby are all due to return shortly as well, to boost their respective clubs (via PhysioRoom.com).