Anderson went off the field before tea, and so was unable to bowl for periods on Friday.
Cardiff: England faced an anxious wait after spearhead seamer James Anderson went for a scan on back and side injuries following the end of the second day's play of the first Test against Sri Lanka.
Anderson went off the field before tea, and so was unable to bowl for periods on Friday but was back in the middle at stumps as a nightwatchman after England captain Andrew Strauss was dismissed shortly before the close.
The hosts were 47 for one at the finish in reply to Sri Lanka's first innings 400, a deficit of 353.
Ashes batting hero Alastair Cook was 24 not out and Anderson, who still led Enlgland's attack with three for 66, unbeaten on one here at Sophia Gardens.
Fellow England seamer Stuart Broad said Anderson's injury, picked up before tea, was a worry.
"Obviously, it's a huge concern for us," Broad, whose Ashes and World Cup campaigns were cut short by similar problems, told reporters.
"He felt a bit of tightness in the back and side. Obviously I know what side injuries are all about after this winter and when you get a little bit of pain it's not great.
"We're being cautious. He's going to go and get a scan this (Friday) evening and hopefully that will come back clear and he'll be OK to go because he's a hugely vital bowler for us."
Broad added batting was unlikely to aggravate Anderson's injury.`
"When I had my side injury I could do pretty much everything but bowl. It is one of the frustrating ones as a bowler.
"An extensive pull shot might strain it or something but we don't really see Jimmy playing a huge amount of them, he's more of a clip to fine leg man."
Broad took two for 113 on Friday and in the process became the second youngest England bowler, after Ian Botham, to take 100 Test wickets.
"I'd prefer it to have come at 90 for one not 370 for eight but it was hard work out there."
This is only the second Test to be played in Cardiff, following the drawn 2009 Ashes opener, and Broad said he hoped his team could do to Sri Lanka what Australia did to England two years ago.
"We got 420-odd against Australia in 2009 and we were still under the pump for the last 120 overs.
"That's got to be our mindset really: do what Australia did to us, try and bat big and bat once then hopefully Swanny (off-spinner Graeme Swann) will be in the game on the last day."
Prasanna Jayawardene's 112 was the cornerstone of Sri Lanka's total and the wicket-keeper was understandably elated to have scored a hundred in his first Test in England.
"This is my first Test in England so I am very happy," he said after batting for more than four hours. "I love handling pressure.
"This is a new challenge but the management trust me and I showed that," he insisted of his promotion to No 6.
Broad added: "We are still in a decent position but Sri Lanka batted fantastically well in foreign conditions and applied themselves brilliantly."