Chelsea's chronic injury list has lengthened further after Frank Lampard was ruled out for up to a month with a torn thigh muscle, an absence which could persuade manager Avram Grant to seek the Croatia and Dinamo Zagreb midfielder Luka Modric's signature during the January transfer window.

Lampard sustained the tear to his right thigh midway through the first period of the riotous 4-4 draw with Aston Villa at Stamford Bridge on St Stephen's Day.

The England midfielder, whose goals have been so pivotal to Chelsea's title challenges in recent seasons, underwent a series of scans yesterday on the injury with the results confirming he will play no further part in the club's busy fixture programme over the festive season.

The 29-year-old will miss games against Newcastle United, Fulham, Tottenham Hotspur and Birmingham City as well as the FA Cup third-round tie against Queens Park Rangers and the first leg of Chelsea's League Cup semi-final against Everton, with the club hopeful he may be fit to return for the second leg on January 23rd.

"Scans have revealed a tear in Frank Lampard's right thigh," confirmed a club spokesman. "The tear is not in the same leg that Frank injured earlier this season. He will begin his rehabilitation immediately and we hope to have him back playing within a few weeks."

While the loss of a key player in Lampard would represent enough of a blow, it has merely compounded Chelsea's problems. John Terry is still absent after breaking three bones in his foot during the defeat at Arsenal earlier this month, Florent Malouda has a knee complaint, while Didier Drogba has yet to return from knee surgery and, should he prove his fitness, will miss up to four weeks in the new year with the Ivory Coast at the African Cup of Nations.

The tournament in Ghana will also prompt the departures of Michael Essien, Salomon Kalou and Mikel John Obi. Ricardo Carvalho, meanwhile, will miss the club's next three games after his dismissal against Villa for a two-footed lunge on Gabriel Agbonlahor.

Chelsea have appealed to the English FA against Ashley Cole's last-minute dismissal for handball on the goalline - the England full back will learn today whether that appeal has been successful - but he, too, is currently due to sit out tomorrow's game against Newcastle at Stamford Bridge.

Aston Villa have also appealed against Zat Knight's red card, awarded after his tackle conceding the penalty from which Andriy Shevchenko trimmed Chelsea's deficit to 2-1. The Villa defender will also discover the FA's decision today.

Against Villa, Chelsea conceded four goals in a game for the first time in exactly four years, since the St Stephen's Day beating for Claudio Ranieri's line-up at Charlton in 2003. Apart from the missing Terry, Grant's defence was at full-strength in the Villa match.

Results have been reasonably good under Grant but his side lies seven points off the lead in the Premier League and the gap could expand by the end of the holiday season.

The Chelsea manager is, however, refusing to raise the white flag and has steeled his side for the hardship ahead. "As long as we have a chance we will do everything we can to catch Manchester United and Arsenal," he said. "We have character and will not give up. We will do anything to challenge them.

"This job has been a big challenge from the day I started it and I will accept this latest challenge."

The London club's situation has left Grant to consider how best to prioritise additions to his squad when the window opens on January 1st. The new manager was always likely to be busy during the month of trading as he begins to shape a team he inherited from Jose Mourinho into his own.

Interest is retained in Bolton's Nicolas Anelka, with a potential move for Modric also now more enticing to bolster numbers in midfield.

"I was hoping to use the transfer window, but now, because of the suspensions and injuries, as well as the African Cup, I must think about using it more," said Grant.

The Croat, so impressive in the 3-2 defeat of England at Wembley last month, has long been on Chelsea's radar. It had been expected that Modric would move at the end of the season - Lampard, after all, has suspended talks over a new contract until the summer prompting uncertainty over his long-term future at the club.

The Dinamo Zagreb vice-president Zdravko Mamic, who also acts as Modric's personal manager, returned to London on St Stephen's Day and intends to hold talks with numerous Premier League clubs over his player's future over the next few days.

Arsenal, Manchester City and Tottenham would compete in that pursuit, though Chelsea remain favourites to secure the 22-year-old for all that they would be reluctant to match Dinamo's €27 million valuation.