Mehidy was struck while he was being interviewed. "He seems OK, he seems fine," coach Steve Rhodes said. "There was no blood or anything like that. I would imagine the physio would check him over for something like concussion because that's normally the done thing."
Mehidy has been a key part of Bangladesh's success in the tournament, taking five wickets.
Pakistan clung to slim hopes of making the semifinals and ended South Africa's chances in a 49-run thumping victory at Lord's.
After losing narrowly to New Zealand on Wednesday, South Africa appeared ready to trudge home in a largely downbeat display. Pakistan scored 308-7, and South Africa's batting struggles were underlined again when it petered out on 259-9.
Pakistan's second win in six matches kept it in the playoffs hunt, three points behind England, with unbeaten New Zealand next in its sights on Wednesday.
The Proteas slumped to a fifth defeat and a washout in seven matches. With two matches to go, their misery is officially over, after winless Afghanistan. Though this is the worst-affected World Cup because of rain, nothing has appeared damper than performances from South Africa, which has failed to make the playoffs for only the second time.
South Africa was 138-4 after 30 overs in its increasingly vain chase of 309 to beat Pakistan at Lord's.
The run rate was below five, with more than eight needed, and all of the top order gone.
Captain Faf du Plessis was out for a 79-ball 63, top-edging fast bowler Mohammad Amir in the 30th over.
Rassie van der Dussen was on 17 and David Miller on 1.
Amir and Shadab Khan had two wickets each.
Amir trapped Hashim Amla on 2 with his first ball in the second over, and Shadab, who had two expensive wickets in his previous two innings at this World Cup, dismissed Quinton de Kock (47) and Aiden Markram (7).
Du Plessis and de Kock steadied the innings with a stand of 87 but the more aggressive de Kock was undone by spin, again.
New Zealand has been fined for a slow over rate against the West Indies on Saturday in Manchester.
Match referee David Boon ruled New Zealand was one over short of its target. Captain Kane Williamson admitted to the offence after the match won by his side by five runs.
In line with set sanctions, Williamson was fined 20% of his match fee and his teammates 10%.
If New Zealand commits another minor over rate breach during the tournament with Williamson in the side, it will be deemed a second offence by him and he will face a suspension.
Pakistan put up 308-7 against South Africa after an 89 by the recalled Haris Sohail in a late flurry at Lord's.
Haris, brought back for the dropped Shoaib Malik, featured in partnerships of 81 with Babar Azam and 71 with Imad Wasim.
He was out on the penultimate ball, his 59th of a superb innings that included three sixes and nine boundaries. Pakistan started the 40th over on 217-3 but Haris ensured a challenging total was set.
South Africa failed to overcome 311 by England and 330 by Bangladesh in its first two matches.
Pakistan was 133-2 after 25 overs against South Africa at Lord's.
Both openers were gone after an 81-run stand, both dismissed on 44 each by legspinner Imran Tahir.
Babar Azam was at the crease on 25, and Mohammad Hafeez on 17, having just survived a strong lbw appeal off Tahir. South Africa lost its review. Hafeez was also dropped on 2 by wicketkeeper Quinton de Kock off Tahir.
Fakhar Zaman and Imam-ul-Haq thrashed South Africa pacemen Kagiso Rabada and Lungi Ngidi to race out of the blocks.
But Tahir got Fakhar to scoop to first slip in the 21st over, and Imam was brilliantly caught one-handed by Tahir diving low to his right.
Spinner Imran Tahir has removed both Pakistan opening batsmen to become the leading South Africa wicket-taker in Cricket World Cups.
The two wickets gave him 39, one more than fast bowler Allan Donald, who retired after the 2003 World Cup.
Tahir, the oldest man in the tournament at 40, induced Fakhar Zaman to lob a catch to first slip in the 15th over, and brilliantly caught Imam-ul-Haq off his own bowling in the 21st. Pakistan was reduced to 98-2.
Tahir, as always, celebrated by running around the Lord's ground with arms out like he was flying.
He has 10 wickets in this tournament.
India captain Virat Kohli has been fined 25% of his match fee for excessive appealing for an lbw decision in the win against Afghanistan at Southampton on Saturday.
Kohli admitted to breaching the code of conduct and accepted the sanction proposed by match referee Chris Broad.
During the 29th over, Kohli advanced toward umpire Aleem Dar in a manner Broad considered aggressive. India was under pressure, and Kohli was animated by Jasprit Bumrah's strike of Rahmat Shah's pads. India had lost its review. Bumrah eventually dismissed Shah in the same over, and Hashmatullah Shahidi, to turn the tide.
Kohli received one demerit point, the second of his career since the code was revised in September 2016. The other was issued in January 2018 during a test against South Africa in Pretoria.
Pakistan won the toss and chose to bat first against South Africa at Lord's.
Pakistan made two changes from its defeat to India last weekend, bringing in batsman Haris Sohail and bowler Shaheen Afridi for Shoaib Malik and Hasan Ali.
South Africa was unchanged after its narrow loss to New Zealand on Wednesday.
Captain Faf du Plessis said he would have chosen to bowl, anyway.
Pakistan: Fakhar Zaman, Imam-ul-Haq, Babar Azam, Mohammad Hafeez, Haris Sohail, Sarfaraz Ahmed (captain), Imad Wasim, Shadab Khan, Wahab Riaz, Mohammad Amir, Shaheen Afridi.
South Africa: Hashim Amla, Quinton de Kock, Faf du Plessis (captain), Aiden Markram, Rassie van der Dussen, David Miller, Andile Phehlukwayo, Chris Morris, Kagiso Rabada, Imran Tahir, Lungi Ngidi.
Pakistan needs a win more than South Africa from their Cricket World Cup group match at Lord's on Sunday.
Both teams have won only once, but Pakistan has a match in hand and a slightly better outside chance of making the semifinals.
South Africa's chances are remote, and gone if it loses.
Pakistan is coming off a thumping from India a week ago. South Africa lost in the last over to New Zealand on Wednesday.
South Africa has a 3-1 win-loss record against Pakistan in World Cup history.
Spinner Imran Tahir needs two more wickets to surpass Allan Donald as South Africa's leading wicket-taker in World Cups. Donald has 38. Tahir is the only bowler here not to have been hit for six. He's delivered 282 balls.
Fast bowler Mohammad Amir has 13 wickets for Pakistan at this World Cup, at an average of just 13.
The forecast is for cloudy but warm conditions.
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